Screwed by Tolerances

Well screwed:A customer had a bracket that needed assembly. The unit used four self-tapping screws to hold it in position. The wrong disk washer bolt type was used, but that's only part of the problem. With hand assembly everything went together and the simple assembly fixture worked pretty well.

Then the production rate went up and the demand rose to about 90,000 units per month. It was time to automate, and instead of starting the screws with an operator, four automatic drivers (on fixed centers) were attempted. After many "machine caused" rejects, the parts were inspected.

Stamped parts with tolerances hole to hole mate quite nicely, but not when located on the part profile. The interference in the holes caused the screws not to start through the holes and jam in the self-feeder drivers.

Part of the problem is the way the parts were drawn and the way the holes were referenced. But a big part of the problem is a supplier that used up all the tolerance in the drawing to make up for differences in bend radius, material changes, spring-back, and take up. Selecting a supplier that was ISO qualified and could certify all the parts would be a help, but part of the issue is poor drawings and no Cpk spec on the incoming product. These are the manufacturer's problems.

The drive to lower cost parts delivered faster and with higher quality is not going to stop. The first step to being the manufacturer that can deliver better, faster, cheaper is under

standing that good parts start with good drawing and solid specifications. Responsibility for this issue falls on both the consciencious manufacturer and the qualified supplier.

We welcome your comments and criticisms, so PLEASE tell us what you think.

From Manual to Automatic assembly

Recently I worked on a project to assemble sheet metal parts with rivets. Several noteworthy aspects of this project come to mind. The first being the fact thay because people can put the parts together doesn't mean that they can be asseembled automatically.

Stamped parts that are punched and THEN formed can only be located from the stamped details; the profile or outer edges are subject to the variances of material thickness as well as hardness (springback). The customer thought that because workers could locate the parts and line up the holes for riveting, fixturing and automation could do the same but with a real reduction in labor cost: until we reviewed the part tolerances.

The tool maker had negotiated tolerances that were easy for him to meet, but in a review of the two making holes and their respective mating surfces, there was +/- over a half a hole diameter in the tolerance. So, if you locate the part, even on punched features, the holes only line up about half of the time. Okay, let's locate the mating parts when they are loaded by placing thme over pins that retract as the rivet is installed into the hole. THis worked for two of the holes, but not for all the holes. There was no way to locate the two pivot points from the inside of the parts without a piece of "loose" tooling. This was unacceptable to the customer.

The parts had an assembled tolerance of +/- 0.4 degrees and the customer required a Cpk of 1.333 on the assembled critical dimensions. The downtime requirement was very low and the requirement for efficiency was 99%+ at a rate of 360 parts per hour. The budget was tight and finally the recommendation to the customer was to load/unload the parts with operators. Install the easy rivets over retracting pins and then install the rivets in the positions with location problems manually. Inspection was to be automated.

The system generated an overall throughput increase of about 20% and had a cash payback of about 14 month based on labor savings alone. The customer was not please with the solution, and cancelled the contract. Sometimes you just have to walk away from a project if it is really not possible.

I would like to hear from any on you who have installed Pop Rivets into blind hole with no pins to line up the holes. In this case because of the way the parts are formed, all the rivets had to be install from the beakout side ir sharp edge of the stamping making getting into the hole even tougher. Do any of you out there have similar experiences that you'll share?

New Products: Inventions, Widgets, Design for Manufacturing

Let me begin by congratulating Wessss for his never
ending entrepreneurship and spirit to help all of us by
creating this blog site. His credentials and leadership
on latest projects speaks for itself.

To our followers: BadVibes, the medication is not working,
try a little extra skin cream to get back to the youthful
look I remember.
Keith, thank you for special efforts on recent projects,
no matter how many times the diameter changed.

Regarding project creations..............
Diversification and added knowledge will prevail in today's
manufacturing business whereby we all will conquer the
economy change. Networking with others is the key to
success to arrive with new clients and vendors for
features and parts needed.

It may be different regarding the way we do things.
Yet the individual steps taken are identical.
We still design, maybe with better software for
solid modeling and surfacing, to prototype parts by way
of SLA techniques. The project itself still needs 2d assembly
drawings, BOM and detail drawings with specifications.

The Design and The Project Plan is the road towards
the goal we want to achieve.
Sit and think is good, but you have to get started.

We still build plastic injection molds, die cast dies,
progressive metal stamping dies and form stations,
fabricate metal, weld, rivet, assemble with nuts and bolts;
machine parts out of steel, aluminum and brass.
We still assemble products with special machinery and
complete assembly lines.
Nowadays robots are added to reduce labor cost and
repetitious intensity. Some mechanical functions are
taken over by electronic equipment,
special valves and sensors to prevent failure.

If you need advice, new ideas and methods to succeed in
your project venture please write us or add a comment
regarding the difficulty you have. We will provide the missing
link and guide you towards success.

Design & Development

Innovation and Value creation

I recently attended a meeting of the the American machine tool trade association. The organization is called the Association for Manufacturing Technology or AMT. The industry is down this year, largely as a result of the economy. The Association and all its members are looking for ways to generate revenue. I was fascinated with a presentation that made the point that manufacturing is the only way to generate revenue producing products that are transportable through time and space. A "widget" made here has a value and it can be shipped anywhere, anytime and it will always have a value.

The presentation went on to demonstrate that if the resources available to make "widgets" are fixed, the only way generate more revenue is through higher productivity, or Innovation. The machine tool industry is all about productivity enhancement; higher speeds, faster feeds, easier programming, and unattended operation, all to improve productivity. But, the low cost solution for revenue growth just might be Innovation. Clever ideas and creative vision can both increase productivity and launch new "widgets" with more function and more features that more people are willing to buy.

The incubator for American ingenuity has long been small business and it's no different for manufacturing. The American entrepreneur has been coming up with better ways to build products faster, better, and cheaper since before the industrial revolution. It wasn't really easier in the old days, but the global economy has changed the landscape of the competitive market place. With foreign countries subsidizing labor and materials as well as assisting in the penetration of key markets, the small and emerging manufacturing companies in the USA need to change the way that they have traditionally worked.

To be an entrepreneur has long meant that you were your own boss, the captain of your ship, and that command was often a lonely thing. Today's demand for competitive prices has driven overhead down so that internal resources are often not available. The company with the clever concept, may not have the engineering staff to design it, the manufacturing know-how to build it, or know where to find the help to bring the idea to market and create the value and sustainable growth that the innovation should bring. Today's business leader needs to find ways to network in order to find manufacturing solutions that make dollars and sense.

Being the "Captain of your own ship" can no longer mean steering the boat with no help. Finding the right part, or partner to help create the solution is more important than ever, because getting to market with the right idea at the right price is a matter of timing. As some wise old guy once said "The Opportunity of a Lifetime must be seized within the Lifetime of the Opportunity".

Without knowing where to find the pedal, the "right" material for the rod, or how to   mold the seat, America would still be standing and waiting.

Innovation @ Work