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Keywords:Mechanical design, engineering, principles, advanced, art, qualitative, quantitative
The Art of Mechanical Engineering Design
by
Lawrence J. Kamm
Consulting engineer, former President of MOBOT
Corporation
Other books by Lawrence Kamm:
- Designing Cost-Efficient Mechanisms
- Real-World Engineering
- Understanding Electro-Mechanical Engineering
- Adventures Of An Entrepreneur
Click here to see the author's track record and qualifications.
Caution
Preface
This is a book for employed engineers and designers. It will make you better at your work and will help you get job security, raises, and promotions. It is the result of my half century as an employed engineer and as an employer of engineers. Some of it deals with responsibilities you may find boring and prefer to leave to others. Or fight about with your boss. But if you shoulder them you will get that job security and those raises and promotions. And feel pretty good about yourself too.
TABLE OF CONTENTS
Chapter 1. Qualitative and Quantitative Design
Chapter 2. The Elements of Qualitative Design
- Imagination
- Judgement
- User interface
- Maintenance
- Abuse
- Materials
- Processes
- Aesthetics
- Specifications & Standards
Chapter 3. Principles of Engineering Design
Chapter 4. Classification of Products
By Quantity
By Type
- Models: Test Of Principle (TOP)
- Models: Visualization (dummy)
- Models: Test
- Short run production
- Quantity production
- Customized production
By customer
- Your own organization
- Factories or institutions
- Special machines built to order
- Quantity products
- Military or Commercial
By user skill, training, and motivation
Chapter 5. Cost and Cost Reduction
Chapter 6. Selecting Materials
Chapter 7. Designing for Manufacturing Processes
Chapter 8. Experimental Design
Chapter 9. Design Organization
Chapter 10. Quality
Chapter 11. Underlying Electro-mechanical Phenomena
Chapter 12. The Humble Switch
Chapter 13. Transducers
Chapter 14. Motors and Generators
References
Table of contents, Selections, from, Part 3 Topics in Design
Engineering
Chapter 10 Designing With Uncommon Manufacturing
Processes
10.1 List of Processes
Chapter 11 Manufacturing Engineering
11.1 What Is Manufacturing Engineering?
- 1. Standard Machines
- 2. Special Machines for Sale
- 3. Special Machines For Your Company
- 4. R&D
- 5. Tool Design
- 6. Planning and Scheduling
- 7. Maintenance
Chapter 13. Transducers
Chapter 14. Motors and Generators
References
Table of contents, Selections, from, Part 3 Topics in Design
Engineering
Chapter 10 Designing With Uncommon Manufacturing
Processes
10.1 List of Processes
Chapter 11 Manufacturing Engineering
11.1 What Is Manufacturing Engineering?
- 1. Standard Machines
- 2. Special Machines for Sale
- 3. Special Machines For Your Company
- 4. R&D
- 5. Tool Design
- 6. Planning and Scheduling
- 7. Maintenance
References
Table of contents, Selections, from, Part 3 Topics in Design Engineering
Chapter 10 Designing With Uncommon Manufacturing Processes
10.1 List of Processes
Chapter 11 Manufacturing Engineering
11.1 What Is Manufacturing Engineering?
- 1. Standard Machines
- 2. Special Machines for Sale
- 3. Special Machines For Your Company
- 4. R&D
- 5. Tool Design
- 6. Planning and Scheduling
- 7. Maintenance
11.2 Suggestions
- 1. Risk Responsibility
- 2. Technician Work, Engineering Work
- 3. Motivation
- 4. Offices
- 5. Education
12.2 Assembly Kits
12.3 The Benefits of Automation
12.4 Justifying the Cost of Automation
12.5 Policy Questions
Table of contents, Selections, Part 3 Understanding Design, "Understanding Electro-Mechanical Engineering"
- The Science and the Art
- How One Designs
- Minimum Constraint Design
- Design for Manufacturing
- User-Friendly Design
- Accuracy, Adjustment, and Gaging
- Reliability, Defects, Abuse, Failure, and Maintenance
- Barriers, Filters, Conduits, and Valves
- Ecology
- Money
- Cost Reduction and Product Improvement
- Constraints on Design
- People Engineering
- Getting Help
- Design Parameters
- Product Classes and Families
Chapter 1. Qualitative and Quantitative Design
Most books on engineering design are books of parameter calculations. Stress, strength, deflection, oscillation frequency and amplitude, temperature, voltage, current, power, and other parameters are their subjects for mathematical analysis. This book assumes that engineers learned these calculations in their academic courses or on software;and that non-degreed designers take calculation problems to graduate engineers.Academic mathematical and scientific training gives an insight into the behavior of designs which the academically untrained designer cannot hope to match; it makes the person with that training a better designer than that person would otherwise be. However this book deals only with qualitative design so both engineers and designers can understand and use its teaching.
Yet one cannot "calculate a design." For the most part, one can only calculate the parameters of a qualitative design to convert it into a quantitative design. The results of parameter calculation may then suggest changes in the qualitative design, and the process iterates. Inventive design always starts as qualitative ideas, even when those ideas are based on educated insight into mathematical relationships.
One can initiate some designs with a quantitative parametric study to extend the original performance specifications into device specifications (e.g., power, enclosed volume, speed). Such a study can sometimes be expressed as families of curves which enable the qualitative designer to start with many parameters at almost final magnitude.
Yet there are many, many aspects of design which are not subject to calculation at all: Consider "robustness," "aesthetics" and "customer's prejudices," which are only three of many. These non-mathematical components of design are covered by this book.
This book expands on my earlier works on the art of design: "Designing Cost-Efficient Mechanisms," Part 3, "Topics In Design Engineering" and "Understanding Electro-Mechanical Engineering," Part III, "Understanding Design." There is some overlap of subject matter, but only some, and I believe it is worth your time to read both those Book Parts and these essays.
Chapter 2. The Elements of Qualitative Design
Chapter 3. Principles of Engineering Design
Aesthetics- Importance
- Provide speedy operation
- Reduce errors
- Damage to people
- Damage to property
- Reduce fatigue
- Basic rule: Imagine yourself operating the product
- make it easy for the customer to retrofit features to replace damaged covers and to change appearance.
- Conduction
- Ventilation
- Natural (convection)
- Forced (fan)
- Liquid and vapor
- Refrigeration
Heating Design
Seals (See Chapter Barriers, etc.)Seal Design
- General concept
- Gas
- Liquid
- Electricity (insulation)
- People (guards)
- Dirt
- Choice of commercial components
Design to ease making changes in mid-production.
Predict plausible changes
Plan for scheduled changes
- Performance improvements
- Performance defect correction
- Addition and subtraction of features
- Solving problems in manufacturing
- Solving vendor problems in materials or processes
- Cost reduction
Improving existing products
Why?
- Meeting and beating competition
- Meeting new customer specs.
- Meeting new government and trade association specs.
- Evading patent and trademark infringement
- Benefiting from newly acquired patent rights
- Adapting to a new merger
- Scaling
- Changed proportions
- Adding and subtracting features
- Changing materials
- Changing components
- Changing performance ratings
- Modularizing
- Cosmetics and fashion
- Changing maintenance needs
- Reducing costs or increasing performance at increased costs
- Adding or reducing models and sizes ("preferred number series")
- Simplifying product and processes
Trade names and design style
Commercial value
Group Technology
- Part families
- Company part catalog
- Company coding system
- Company material catalog (raw material and preferred purchased parts)
- Company process catalog
- Use of computer. Cad retrieval and modification.
Minimum Constraint Design
This subject covers four pages in Successful Engineering and 102 pages in Designing Cost Efficient Mechanisms.
- General Description
- Degrees of Constraint
- Theory of MinCD
- Semi-MinCD
- Useful RedCD
Use of Commercial Components
{This subject covers 56 pages in Designing Cost Efficient Mechanisms. Parts (fasteners, seals, bearings, gears, belts, etc.) Assemblies (Clutches, transmissions, motors, controllers, etc.) Overall product function and configuration
Modifications through product life
Specifications and proposed changes in them
Packaging and Shipping
Ease of disassembly and reassembly before and after shipment
Shipping mode
Reliability and Maintenance
- Deterioration modes
- Improve resistance to abuse, human and environmental
- Use preferred components
- Fail-safe, fail-soft
- Different service requirements
- Kinds of maintenance
- Accessibility for maintenance
- Built-in diagnostics
- Reliability improvements
- Testing
- Suiting the service people
- Predicting wear-out; planning spares
Mechanical
- Shape and dimensions
- Stress distribution
- Strength
- Stiffness/rigidity, and distribution
- Weight, and distribution
- Hardness/wear resistance/abrasion resistance
- Ductility
- Toughness
- Coefficient of friction/lubricity
- Damping
- Creep
- Fatigue
Electrical
- Conductivity/Resistivity
- Dielectric constant
- Dielectric strength
- Magnetic permeability, saturation, eddy current loss, hysteresis loss
- Electromagnetic forces
- Electrostatic voltages
- Corrosion from leakage currents
Thermal
- Thermal expansion
- Temperature resistance, high and low
- Specific heat
- Thermal conductivity
-
Chemical
- Chemical resistance, including corrosion
- Chemical harmfulness, including pollution by process and product
- Adhesive and surface finish bondability
- Hygroscopy
- Porosity
- Fading
Biological
- Toxicity
- Fungus resistance
Optical
- Transparency, translucence, opacity
- Color
- Refractive index
Prejudices of:
- Engineering management
- Manufacturing department
- Sales department
- Distributors
- Customers (and their departments)
Competitors
- Who
- What wins
- Predicting
Iteration and Convergence
- When to stop changing
- When to resume changing
Chapter 3. Kinds of Products
By Quantity
By type:
- Models: Test Of Principle (TOP)
- Models: Visualization (dummy)
- Models: Test
- Short run production
- Quantity production
- Customized production (color & feature combinations)
By customer
Your own organization (Products for in-house use)
- Simple tools
- Production machines
- Research machines
Factory or institution
Special machines built to orderQuantity products
Military or Commercial?Customer skill, training, and motivation
- Unskilled renter
- Consumer
- Technician
- Professional
Chapter 4. Cost and Cost Reduction
Product life cost of a part is the sum of:- Per unit material cost (including scrap)
- + Per unit vendor services cost
- + Per unit labor cost (with overhead)
- + Pro-rata replacement cost to the customer
- + Pro-rata reject and rework cost
- + Amortized R&D, including market studies
- + Amortized tooling cost
- + Amortized setup cost
- + Amortized capital equipment cost
- + Amortized expendable tooling cost
Product life cost of a product to the customer is the sum of:
- Purchase price
- + Operating cost (labor, power, supplies)
- + Maintenance cost, including the cost of downtime
Industrial and military customers are more rigorous in estimating product life cost than are most consumers, but if you watch advertising, read consumer product research magazines, and listen to gossip, you will discover that many consumers also think about product life cost, even if they do not know the phrase.
There is an invisible cost: the additional cost of parts and assembly, and of limited product value to its customer and consequent fewer sales, which result from poor design.
As a designer, you may feel that most of these costs are not your problem. They are. You are paid by your employer to design products which will bring him profits and each of these items directly influences those profits. Guess what will happen to your pay, job security, and prestige if your manager knows that you always have all of these in mind.
Effects of JIT (Just In Time) policy:
- Batch size.
- Tool cost.
- Setup cost.
- A. Existing product part refinement, no changes in other parts are permitted.
- B. Next generation product (new model); changes in associated parts are permissible.
- C. New product under design; any changes are permissible, subject to progressive design freeze.
Ways to reduce cost
This is a guide and check list for hard thinking by you. There are no cookbook formulas.
- Design for cheaper material.
- Design for less material, including less scrap.
- Design for automatic fabrication.
- Design for unconventional manufacturing processes if they reduce overall costs.
- Design for automatic assembly.
- Design for tooled processes instead of manual work.
- Design the packaging as part of the product design. [32]
- Design for fewer parts. Combine several parts into one, including fasteners.
- Design for fewer fasteners.
- Design for assembly without reworking parts to fit.
- Design for available assembly skill (e.g. skilled single assembler working from a kit of parts vs. unskilled line assemblers.)
- Design common parts for different models and products.
- Design several parts to use the same tooling ("Composite Components")
- Relax unnecessarily close tolerances. Reconsider "Standard Tolerances."
- Re-distribute tolerance budgets.
- Re-consider the interchangeability policy:
- The assumption that any part must fit as made
- Selective assembly (e.g. high precision ball bearings)
- Modify part to fit. Selective re-work.
- Modify part to suit its manufacturing process: Change tolerances which do not affect fit. Correct corner radii, fillet radii, tapers (draft), thickness, thickness variations and junctions or transitions, and details of material specs.
- Modify, add, or subtract mating features of mating parts to ease joining of parts.
- Consult your Industrial Engineer and Manufacturing Engineer to select process and to estimate cost ("Concurrent Engineering").
Chapter 5. Selecting Materials
This chapter helps you select a material in three ways:1. Comparison of properties of different materials,
2. For many types of part, specific materials are suggested, and
3. A material classification list to scan when thinking about materials.
1. Comparison tables
{These are adapted from the annual Materials Selector issue of Materials Engineering. Bralla has similar tables, but with many fewer entries.}
Mechanical Properties
- Density
- Modulus of elasticity in tension and in shear
- Tensile and shear yield strengths
- Ultimate tensile, compressive, and shear strengths
- Elongation of metals
- Specific strength
- Fatigue data
- Specific stiffness
- Hardness of metals, ceramics, plastics, and elastomers
Thermal Properties
- Coefficient of thermal expansion
- Heat deflection temperature, plastics
- Maximum service temperature, non-metallics
- Specific heat
- Thermal conductivity
Electrical Properties
- Resistivity
- Dielectric strength
- Dielectric constant
Chemical properties
- Corrosion resistance
- Electrochemical activities
2. Selection guide, by type of part, listed alphabetically by part name:
{A long list of typical parts, adapted from the "USES" sections of Materials Selector, for example:}
. . . Gears, instrument Aluminum alloys xxxx, yyyy Stainless steel alloys zzzz, aaaa Gears, high strength Carbon steel alloys bbbb, cccc Alloy steel alloys dddd, eeee . . .
3. Classification of Materials
- Metals
- Ferrous
- Cast iron
- Carbon steels
- Alloy steels
- High strength steels
- Stainless steels
- Soft magnetic steels
- Non-Ferrous
- Aluminum
- Copper
- Copper alloys
- Brass
- Bronze
- Beryllium copper
- Zinc
- Magnesium
- Titanium
- Cobalt
- Beryllium
- Tin
- Nickel
- Lead
- Tungsten
- Precious
- Silver
- Gold
- Platinum
- Palladium
- Ferrous
- Mill Processed Metals (In warehouse inventory)
- Rolled shapes
- Extruded shapes
- Drawn shapes
- Treadplate
- Perforated sheet
- Expanded sheet
- Galvanized sheet
- Preplated sheet
- Embossed sheet
- Woven wire
- Deformed bar ("rebar")
- Sintered porous bronze and aluminum
- Shot
- Thermoplastics
- Polypropylene
- Polyethylene
- Polystyrene
- Vinyl
- ABS
- Acrylic
- Nylon
- Acetal
- Polycarbonate
- Cellulosics
- Fluorocarbons
- Thermosetting plastics
- Phenolic
- Polyester
- Melamine
- Urethane
- Epoxy
- Alkyd
- Diallyl phthalate
- Elastomers
- Rubber, natural
- Butyl
- Silicone
- Fluorocarbon
- Polysulfide
- Neoprene
- Styrene butadiene
- Nitrile
- Organics
- Wood
- Fiber
- Paper
- Leather
- Cork
- Inorganics
- Mica
- Carbon
- Graphite
- Concrete
- Plaster
- Mortar
- Glass
- Silica
- Soda lime
- Lead
- Ceramics
- Alumina
- Magnesia
- Beryllia
- Carbide
- Nitride
- Steatite
- Adhesives
- Thermosetting
- Thermoplastic
- Inorganic
- Solders
- Tin-Lead alloy
- Silver alloy
- Copper alloy
- Composites
- FRP (Fiber Reinforced Plastics)
- Glass fibers
- Graphite fibers
- Boron fibers
- Whisker reinforced
- Cork and rubber
- Friction materials
- Glass bonded mica
- FRP (Fiber Reinforced Plastics)
- Semi-finished materials
Laminates
- Plastic
- Wood
- Metal
- Formica (printed)
- Honeycomb
- Surface coatings
- Paint
- Electroplating
- Anodizing
- Conversion coating
Chapter 6. Designing for Manufacturing Processes
See Bralla reference for detailed descriptions and different varieties of these processes and for design rules for each.Process availability
- Those available in house
- Those available at regular vendors
- Those which are new to your company
- Buy new equipment?
- Find new vendor?
Processes by category: 1. Convert amorphous material to parts:
- Casting (Metals, plastics, elastomers, ceramics & glass)
- Sand
- Permanent mold
- Rubber mold
- Investment
- Die
- Centrifugal
- Molding (Plastics, elastomers, and composites)
- Compression
- Transfer
- Injection
- Blow
- Powder metallurgy pressing and sintering
- Electroforming (Metals)
- Extrusion Metals, plastics, elastomers
- Flame spray buildup Flame Plasma arc
- Vacuum deposition (Metal films on anything)
- FRP layup
- Open
- Die
- NC/UV plastic forming
- Glass blowing
- Potter's wheel buildup: Ceramics
Mill Products
- Flats
- Rounds
- Tubes
- Rolled shapes
- Extruded shapes
- Drawn shapes
- Deform
- Forge
- Coin
- Upset
- Impact extrude
- Emboss
- Hob
- Peen
- Cut
- Shear
- Saw
- Burn
- Flame
- Plasma Arc
- Laser
- Water Jet
- Wire electrode EDM
- Machine
- Turn
- Mill
- Broach
- Make holes
- Trepan
- drill
- bore
- counterbore
- ream
- burnish
- hone
- tap
- grind
- Abrade
- Grind
- Surface
- center (OD & ID)
- centerless
- double disc
- thread
- contour
- Sand
- Hone
- Lap
- Polish
- Grind
- EDM (shaped electrode)
- Bend
- Brake
- Die
- Roller
- Stretch
- Press
- Pierce
- Blank
- Draw
- Spin
- Swage
- Chemically mill
- Heat treat
- Tumble (clean, de-burr)
- Shot peen
- Sand blast
- Electroplate
- Anodize
- Paint
- Chemical conversion coat
- Etch
- Porcelain enamel
- Flame or arc spray
- Abrade (rough pattern to high polish)
- Clean (Sand blast, wash)
- Deburr (Hand tools, tumble, flame)
- Destructive: Stress to specification or to failure
- Non-destructive
- Measurement
- Manual instruments, one measurement at as time (mechanical, pneumatic, & electronic, millwright techniques.)
- Multiple measurement gages
- Automatic measuring machines
- Go-no go gages
- Optical comparator
- X-ray
- Neutron beam
- Stress-coat
- Magnetic particle
- Fluorescent dye
- Gear checker
- Surface comparator
- Electrical, magnetic, and optical instruments
- Measurement
- Statistical Quality Control
- General discussion
- Manufacturing cells
- Weld
- Gas
- Arc
- Laser
- Electron beam
- Spot
- Friction (spin)
- Thermite
- Explosive
- Solder
- Soft
- Hard
- Diffusion bond
- Adhesive bond
- Rivet or roll
- Swage
- Press
- Hammer
- Electromagnetic
- Press fit
- Joining with fasteners
- Threaded
- Quarter turn
- Spring clips
- Friction ties
- Joining by interlocking features
- Rigid
- Elastic latching
- Combination (Interlocking plus fasteners)
- Electric wire
- Work orders to factory and warehouse
- Work status from factory and warehouse
- CNC data to machine tools
- Template and cam control
- Machine tools
- Contour burners (flame, arc, laser cutting)
- Temperature cycles
- Numerical control (PLC, NC, CNC)
- Machine tools
- Tool changers
- Contour burners
- Temperature cycles
- Plastic part UV precipitators
- Machine tools
- Robots
- Machine loading/unloading
- Fabricating
- Spot welding
- Arc welding
- Part manipulation
- Spray painting
- Adhesive and sealant deposition
- Automatic material handling
- Conveyors
- Automatic guided vehicles (AGV)
- Automatic storage and retrieval systems (ASRS)
- Machine tool cutter magazines
- Transfer machines
- Fabrication
- Assembly, with part feeders (design parts for feeding)
- Automatic testing machines
Chapter 7. Design of Experimental Models
Kinds of experimental models and experimentsDebugging
Chapter 8. Design Organization
Documentation- Drawing numbers
- Parts lists
- Drafting practice
- Dimensioning (including coordinate labeling without arrows.)
- Metric
- Tolerancing
- Fill-in-the-blanks drawings
- Manufacturing instructions
- Specifications
- In-house
- General and legal
- Customer
Chapter 9. Suggestions for Designers
Designer's Hand ToolsCollect "feeling pieces" for guiding design judgement: Samples of different thicknesses of sheet, including a feeler gage set, different sizes of tubing, rod, and the special materials and parts you use.
Have a linear caliper, steel tape, and magnifying glass of your own to examine actual parts without having to call in a technician.
Chapter 9. Quality Our product quality is one way we compete. But "quality" is like patriotism; everyone is in favor of it and claims to have it but when pressed for details many become vague.
Product quality is degree of freedom from defects. Assuring defect free quality is a complex problem and there is never perfection. This article is a guide for managers of engineering, manufacturing, purchasing, and marketing who must make business choices affecting the quality of their products; for customers who must choose among competing products; and for customers who write specifications for special products to be made for them.
Some defects are functional, such as awkwardness, non-uniformity, distortion, or complexity. For example, a handle with sharp edges may work every time but it has a functional defect.
Other defects include outright failures such as broken parts or atypical noise, and aesthetic defects such as ugliness or uneven paint.
Some defects may be intermittent. Some may be sensitive to environment. Some may be sensitive to the way the product is treated or used. Some may be latent and occur after sale. Some may appear as a gradual deterioration. Some may appear as a sudden failure. Some may exist in every copy produced and some may appear in some percentage of copies.
Every defect reduction effort costs money in itself, although it may ultimately reduce overall cost and bring other benefits such as increased sales and prestige. Optimizing cost is one of the basic problems of management.
Slogans about quality and new names for quality control may make effective advertising copy but they do not reduce defects except to the degree that they motivate care in those who create defects. There are actions which reduce defects.
Product capability is not the same as product quality, although it certainly contributes to product value. For example an instrument able to measure many quantities with great accuracy has high product capability but if it fails frequently it has low product quality.
Design and Engineering
Product quality starts here; defects designed into the product will affect all copies made and cannot be compensated by greater effort downstream.
Designing out defects anticipates downstream sources of defect and strive to prevent them. For example a designer may choose to prevent painting defects in the factory and abrasion of paint in service by making a cabinet of molded plastic which requires no paint.
Designing out defects includes providing margins of safety to compensate for variations in materials, components, manufacturing care, inspection, shipping abuse, and use. These margins cost money, size, and weight, so their magnitudes are a challenge to management judgement.
Designing out defects includes designing for those manufacturing processes which produce few defects, and design for inspectability. The designer should consult with manufacturing and inspection personnel.
Designing out defects includes the product's human and physical environments. For example product quality for Army field use is different from product quality for medical research laboratories.
Designing out defects includes designing packaging, instruction manuals, and instruction labels as parts of the product which can constitute assets or defects.
Designing out defects is designing for available low defect materials and components. The designer should consult with purchasing personnel.
Designing out defects takes costly man-hours. Management must decide how far to go.
The product's maintenance plan is part of the product's design. It may be a major quality defect if it does not provide acceptable maintenance. Among management options are:
- Maintenance. Discard and replace defective or worn out products. If the
product is cheap enough and plentiful enough, this may be acceptable.
- Do it yourself maintenance. Provide diagnostic aids, instructions, and
special tools and a convenient source of spare parts and consumables. Battery
replacement is a common example. Design for easy access to encourage the
user to actually perform routine maintenance. Unless customers are persuaded
to follow this plan properly, there is a quality defect.
- Organize dealer maintenance, his place or the customers. Many complex office machines may fail occasionally without being considered of poor quality because a phone call brings an immediate repair man. A delayed response is a quality defect.
Designers are relieved of some responsibility by specifications and codes. But these, too, can be imperfect or not recognize the peculiarities of a particular product, so the designer should critique such rules and protest if they are inadequate to prevent defects.
Design Testing
Even the best designers make errors, so a product design is tested and revised before it enters production. The extent of testing and revision, i.e., their budget, is another management decision which affects the number and kinds of defect in the final product.
Purchasing
Purchasing personnel can reduce product defects due to defective materials, components, or services by choosing and supervising vendors. They face a direct conflict between cost and absence of defects, together with other problems of vendor reliability.
Manufacturing
Manufacturing processes can introduce defects at every step of the way. Ways to reduce manufacturing defects are:
Enhance worker skill and morale.
Perform the work with machines and provide special tools for workers.
Inspect for defects which have been either purchased or introduced in the factory.
Maintain strict discipline in material handling and documentation procedures. MIL and ISO specifications can be followed for these procedures.
Worker skill can be improved by testing job applicants for aptitude and by providing further training to those already employed.
Worker morale may be improved by better labor relations regarding wages, working conditions, and work rules, by treating workers and their suggestions with more respect, and by reducing the division of labor by broadening and diversifying each worker's job.
Work done by machines and tools is typically more uniform than that done by hand. Standard economic justification is required.
Inspection is done by specialized personnel and equipment, but in addition, production workers can be motivated to call out defects they see while performing their production jobs.
Repairing products rejected by inspectors may introduce new defects, so decisions about repair policy must be made. For example, printed circuits may be damaged by heat when replacing components.
Reductions in both product cost and product defects would come from improving the manufacturing engineering department. Improvements can be made in staff selection, further training, pay, authority, and supervision.
Marketing
The marketing department is the interface between the customers and the other departments. Marketers help the other departments please the customers by explaining what pleases and what displeases. It is a management responsibility to make the other departments pay attention to the marketers. Pleasing customers sells products.
Conclusions
Defect reduction requires investment in both money and personal relationships but the successes of our Japanese and German competitors teach that the investments are profitable in the long run.
Return to Table of Contents
Engineering and Science It is the conventional wisdom of laymen that if you want a really great engineer you get a scientist. For example, the presidential commission investigating the Challenger disaster included the great theoretical physicist Dr. Richard Feynman, but no engineers. As a result Feynman, who never heard of O-rings before, was successfully misled in a cover-up and the public never found out that the failure was due to a negligent dimension error in the O-ring grooves and not to low temperature. (See Real-World Engineering, pages 5-7.)
Engineering is neither better nor worse than science, but it is different.
The object of scientists is to understand the behavior of the physical world, to learn the "laws of nature" (better called the "facts of nature," there being no legislation involved.) The object of engineers is to make useful things. Since useful things must "obey" the laws of nature, engineers study science. Since observing nature requires certain useful things - scientific instruments - experimental scientists do a good deal of engineering. Furthermore in some advanced engineering, such as semiconductor devices, science and engineering advance hand in hand; there are teams of scientists and engineers working together and the boundaries between the two activities are blurred and unimportant.
Nevertheless there are major differences between the two fields in both attitude and subject matter. In addition to science and mathematics, engineers study materials and hardware and design: metals and concrete and beams and generators and stills and engines and so on which scientists need not study. The entire attitude of engineers is to build useful things rather than to understand nature. One should no more call upon a scientist to explain why a machine does not work properly than to call upon an engineer to explain a nuclear phenomenon.
Return to Table of Contents
References
- Bralla, Handbook of Product Design for Manufacturing
- Materials Engineering Materials Selector
- Kamm, Successful Engineering S.E.
- Kamm, Designing Cost Efficient Mechanisms D.C.E.M.
- Kamm, Understanding Electro-Mechanical Engineering
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