Sunday, October 11, 2009

Here's an interesting paper by Alex Krulikowski on dimensioning a Feature of Size in ASME Y14.5

I believe that dimensioning and tolerances is the area with the most opportunity for productivity improvements. This is especially true for new products and new organizations where no history of process capabilities and part requirements has been used to optimize the part production.

Wednesday, May 28, 2008

Lean Product Development - A Technology Approach

One issue I've come to appreciate over the years is the difficultly of transferring design information to manufacturing. This difficult task has been further complicated by the introduction of a disruptive technology - 3D computer modeling.

After leaving the relatively defined structure of large corporations, I was involved in setting up an Engineering department at a design consultancy. The lack of complete internal drawing standards was aggravated by the impression of the (mostly young) engineers that the 3D model described the part they wanted built. At that time most of the smaller prototype shops were still using paper drawings with limited CAM.

To address this problem, I developed a white paper "Minimum to Manufacture Documentation" which can be found on my web site. It was used to ensure our prototype shops knew what they were getting and our engineers knew what was expected of them.

My next revelation came while working at a CNC contract machine shop. We would receive design documentation in a variety of forms from 3D models to paper drawings. While a paper drawing usually contained the information required to produce the part, it often required us to build a 3D model to efficiently fixture and process the part. In addition, larger companies often used internal specifications whose meaning were not spelled out. By itself, the 3D model was more efficient but usually did not give us enough information to adequately design the fixtures and process.

I updated the MDM document and also developed a presentation on "Machining Your Part" to discuss some of these issues. The presentation is also on my web site and currently focuses mostly on CNC machining, but I hope to expand it to other processes.

The last piece of this story is my recent attendance at a seminar on Lean Product Development. At the time I was also checking files and drawings on a drive train project. The goal in documenting the dimensions and tolerances is to ensure that the manufacturer has enough information to use the optimum process to produce the part.

It occurred to me that in most instances the desired process had been developed by manufacturing and engineering through years of experience. In fact I was often working backwards, taking what I knew about the desired process and ensuring the dimensions and tolerances were appropriate for it. Looking at it this way the effort to determine the correct dimension and tolerance scheme is not value added, since the real goal is to use a process that gives a quality part.

Let's take the example of a shaft that is press fit into a bearing at each end. In this case I needed to look up the tolerance of the bearings from the vendor. Then I needed to look up the recommended fit of the shaft from the standards. I also needed to determine the geometric tolerance of the bearing surface and shoulder on the shaft from a similar part. When manufacturing receives the files they will look at the drawing and then compare it to a similar part they are making to determine what process is capable of making the part within tolerances.

What we really wanted is a power transmission shaft that would perform adequately and was cost effective to produce. We already knew how to do that but had disseminated the information across several documents in multiple departments.

Why couldn't the designer just select a library feature for a shaft that fits the specified bearing from a CAD pallet and apply that to the part? Embedded in that feature would be the manufacturing process(es) that were known to produce it. The CAM program could recognize the feature and the required process and generate the tool path.

To implement this would require cooperation between engineering and manufacturing - always a good thing. The technology is already there in the major CAD/CAM systems. It would be better if this was developed as a standard so that it could be implemented by any software.

Your thoughts? Reply to this post or email me: david at dmajic dot com

Friday, May 16, 2008

Engineers' Responsibility and the New Media

I was fortunate to attend the 'Reinventing Product Development' seminar held by PTC this month. The presentations were excellent and one stood out because it addressed the myths and mis-information that are being used in the Globalization debate. It turns out that little methodical research has been used to develop the 'facts' presented in this debate and reported by the media as such. Vivek Wadhwa, the speaker, started researching this issue at Duke and has discovered that much of the accepted CW (conventional wisdom) was incorrect, based on facts. You should read this interesting paper; Feeling the Elephant and explore the rest of this site at GlobalizationResearch.

As an Agricultural Engineer, I am extremely interested in the Bio-Fuels debate. I am especially concerned about the recent allegations that Bio-fuel use is causing a global increase in cost of food or even a shortage of food. I have heard several neighbors and acquaintances echo these concerns asserting that this is true. As I researched the issue, I've found that the increase in food prices is primarily due to increased fuel costs and the increased demand in India and China for more food and less energy efficient food (i.e. meats).

I remember listening to a lecture regarding renewable resources last year, where the speaker mentioned that the fossil fuel companies had created a $100MM fund to 'address' the competition from renewable resources. Is it a coincident that food prices are rising due to fossil fuel costs, but the media is blaming them on one of the possible cures for high fuel costs?

Which brings me to the point of this article. The current media environment is one in which anyone with a computer can affect the debate. This 'new media' is inexpensive and dynamic but is not driven by knowledge or dedication to the truth as much as it is by doctrine and self interest. This competition is causing the so-called main-stream media to try to reduce costs and respond to events faster. Unfortunately, the path they've chosen is to reduce quality (sounds familiar to those of us involved in manufacturing during the 70's and 80's). We are faced with societal decisions that can be classified and garbage in - garbage out.

That's were we come in. As engineers we are used to making decisions based on facts and we are skilled at finding the relevant facts. We need to take time to research the important issues of the day so that we can provide thoughtful analysis when presented the opportunity. We need to reestablish the trust that our method of thoughtful analysis is the only way to develop solutions to today's problems. Who knows maybe one day being an engineer will be more important than being a lawyer for a political career.

Have a good week!

Tuesday, April 29, 2008

Learn to Sketch

I got a call from former colleague, Jeff Kennedy, last week. Among other things, he is offering an interesting class for engineers that will teach free hand sketching.

I have to admit that I'm terrible at free hand sketching and have been trying to improve my ability for years. In the 90's I started working with industrial designers and really saw the advantage of being able to describe a concept with a quick sketch. We could sit with a client and turn our thoughts into a picture as we met. And, since a picture is worth 1000 words, we were able to quickly and accurately communicate and document our discussions. The same was true for brainstorming sessions, where the ideas being proposed were understood by all and immediately documented for later review.

I was looking through a book about Leonardo da Vinci and began wondering how much of his creativity was due to his ability to express his ideas in sketches?

Now CAD is a wonderful tool and I especially like how SolidWorks allows the generation of virtual concept models quickly and easily. However, I believe there is a disruption of the innovative thought process, especially in group settings, when using CAD.

So check out Jeff's offering here and if there's interest I will try to put a group together so we can share the cost.

Saturday, April 5, 2008

ANSI Standards should be free!

Why aren't ANSI standards freely available on the Web?

Consulting engineers and designers typically work on projects in a variety of industries. This provides cross-fertilization of ideas that is essential for maintaining our competitiveness in New Product Development. It is difficult for consultants to maintain a library of all the standards that they might require. In addition standards change but there is no mechanism for notifying users that a significant change has occurred.

These problems would be solved by making all ANSI standards freely available on the Web. There would be no need to store a standard either physically or electronically and therefore the current version would always be used. The appropriate standards would be available to all engineers and designers. The biggest advantage might be having the text of these standards available to the search engines. This would improve the chance that a consultant will find the appropriate standard.

The idea of selling the standards is antiquated and counter-productive. It should be changed. What do you think?

Friday, March 14, 2008

CAM and the CAD file

CAD/CAM vendors continue to promote the idea of 'leveraging' the geometric file throughout the process. The unasked question is whether the parametric model can or should be used in the manufacturing process.

Part of the answer depends upon the manufacturing process. Even with additive manufacturing (rapid prototyping) the model is not always used directly but tessellated and sometimes supports are added. This is usually done outside the original CAD software, but is fairly automated.

A properly constructed plastic part can be injection molded using the CAD file, but the mold design is often done with a Mold Design /CAM package other than the original CAD software. The same can be said of other molding processes. Once transferred, the model is seldom parametric and changes must be communicated back to the designer.

CAM vendors have done a lot to integrate with the more popular CAD packages, but often that is just an automated transfer of the static solid model into the CAM software. Certainly the higher end products like Pro-E do integrate CAM into the CAD product. My experience is that the capability of the CNC programmer is more important than the software used.

However, even when the software supports it, is there any true value to the use of the parametric file for Manufacturing? Most CNC programmers feel that they are often better off keeping the manufacturing files separate. This is due to a variety of reasons including the need for geometry changes for intermediate manufacturing steps, errors to the manufacturing process when changes are made to the model, and the administrative overhead required to coordinate a single file. (We’ll discuss PDM at a different time.)

In reality there is a minimal advantage of having a single all encompassing model and there are a minimal number of instances when a single model is truly more efficient. Therefore, I don’t believe that the use of a specific CAD/CAM package from your contract manufacturers should be high on your evaluation criteria. You should care if the vendor has the ability to use your CAD models without conversion, but little else.


Tuesday, March 11, 2008

CNC Machining - Tolerances

How much does a Zero cost?

I have recently given several presentations on how a part is processed in a CNC shop. The talk discussed the decision making process for selecting the right machining process. It also discussed some rules of thumb and showed how to make a design more machinable.

The one issue I struggle with presenting is tolerance. Most engineers understand that a .001" (.025mm) tolerance is going to be more costly than a .01" (.25mm) tolerance. Sometimes,a small change in the tolerance can have a large affect on the part's cost. This is because of process tolerance; that is, each way of doing something will have an intrinsic tolerance.

For example, a total tolerance of .005" (.13mm) is easily obtained by drilling. However, once the tolerance decreases to .002" (.050mm) reaming is required. The time to produce that hole is effectively doubled. If you estimate a $1/minute machining cost this can add $.25 per hole.

It seems that there is no standard way that companies and engineers tolerance their drawings. This is inexcusable because ANSI B54.1 completely describes how this should be accomplished. There are plenty of resources on the Web that reference parts of ANSI B54.1, but for less than $100 you can purchase Machinery's Handbook. I purchased mine on CD-Rom and have the files on my computer, so that it's handy whenever I'm developing a new part.

Later I plan on trying to tie specific tolerance classes to manufacturing cost.