easy to feed
Figure 21.15 Examples of parts climbing or shingling. (From Boothroyd, Assembly Automation and Product Design, Marcel Dekker, NY, 1992.)
We have not yet reached a point where we need a decision process for "automate or conventional build," comparable to "make or buy," but it is coming. Meanwhile, whenever the designer encounters a part or an assembly whose repetitive requirements to make or assemble exceeds 200,000 (project plan quantity times items per end product), he or she should immediately confer with manufacturing engineering to determine any anticipated plans to automate. When the quantity exceeds 1 million, it is almost certain that automation must be used.
Data and books on automation are available in manufacturing and elsewhere. These are illustrated and should be reviewed and studied by designers who encounter parts and assemblies which can or should be automated.
When parts pose unusually difficult handling and orientation problems, experimental mockup stations should be built to verify parts handling processes prior to building the assembly machine. The product designer, the manufacturing engineer, and the tool designer should work as a team through this development state.
- Old design New design
Figure 21.16 Design parts for ease of assembly. (From Boothroyd. Assembly Automation and Product Design, Marcel Dekker, NY, 1992.)
While each part or assembly presents a special problem in automation, some general recommendations and requirements apply,
1. Parts should have at least one axis of symmetry, with ability to fabricate, feed, and assembly in respect to the axis. A sphere is, of course, ideal.
2. Parts should be suitable for sorting and alignment for feeding on equipment such as Syntron or Vibron unit.
3. Dimensioning should be such that inspection gauging can occur from one reference point or axis and one plane of reference.
4. Parts being assembled automatically must be designed to engage with or snap on to mating parts so that they will not shake loose during subsequent assembly sequences. It is impractical to balance parts on one another when using automated equipment.
5. Units being torqued together should have a shaped region such as a square or hexagon to permit grasping and torquing.
6. Messy materials, such as lubricants and adhesives, create machine maintenance and clean-up problems unless the parts receiving them are designed to accept leak-free feed orifices with "no drip," point-of-application cutoff.
7. Semiautomated operations should always be considered whenever the discriminatory capabilities of a human being will result in a significant simplification of the automation equipment.
8. In designing for automatic assembly, the designer should ask the following questions:
Can parts be made symmetrical to avoid orientation problems? Do symmetrical parts have clearly defined polarity features? Are the number of significant part orientations minimized? Will parts tangle?
Will parts nest or interlock, thereby causing problems?
Will the part design cause shingling?
Are critical dimensions and tolerances clearly defined?
Do the parts lend themselves to easy location and assembly?
Does the design have a datum surface for accurate parts location during assembly?
Have all unnecessary handling requirements, such as turning over parts and/or assemblies, been avoided? Does the assembly have components that are buried or difficult to reach and position? Has the design been simplified and standardized as much as possible? Have excessive burrs and flash been eliminated? Can difficult-to-handle parts be assembled in an automatic system?
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