RACKING DESIGNS FOR SMALL PARTS
Q. My apologies for the length of this question. However, I feel you need a full explanation of my dilemma to properly consider this request.
I have recently been promoted to a buying position. Our company sells steel stampings primarily to Tier 1 automotive suppliers. We are outsourcing many of our parts for E-coating to four vendors. Most of our parts are small and fairly light in weight. I estimate the average surface area is about 6–10 in2. We are striving to develop a logical model for making a vendor selection based on the quotes we are receiving for coating costs and fixture charges. We also want to find a way to include processing loss (parts lost in the coating process) and light or no-coat parts, which we are now starting to get a good handle on. I am hoping you can help me understand how to better address this issue.
Let me relate some information about our current study. We are bidding on a new part number. We recently sent out a request for quote on E-coat for that part number to seven E-coat vendors on our approved list. The part is a small bracket with an annual volume of 440,000 pieces and they are to be bulk packed. The typical variety of quotation responses came rolling in. Here are some examples from three vendors with whom we are currently doing business.
- Vendor A quoted a coating price 9% below the mean price for E-coating, plus a $500 fixture charge. Our quality people tell me they use “universal fixtures.” The quality experience with this vendor has been spotty. At times we have had reports from our inventory control people of processing loss exceeding 3%. Also, our quality team has reported parts that appear to have thin coating or even no coating, on 4–6% of the parts.
- Vendor B quoted a coating price of 3% below the mean price and a fixture charge of $850. They are using what they call “adjustable fixtures.” Their recent quality record with us shows an average processing loss of 1.5%. Parts that are not fully coated have been running about 3%.
- Vendor C quoted a coating price 8% above the mean price for E-coating and a fixture charge of $7,500. They explain that their racks are “specifically designed for each part number.” Their record with us shows a processing loss that is essentially negligible. (It is easily less than 0.5%.) Our quality people are telling me that they cannot remember when they saw a part from this supplier with a light coat or no coating.
Based on our quality experience I have recommended we use the Vendor C numbers as we prepare our quote for the project to our customer. Our sales manager and our quality manager both agree. However, our CFO points out the 17% spread in coating price and the $7,000 difference in the fixture charge between Vendor A and Vendor C. She feels that, if our competitors use the pricing from Vendor A, they will surely win the award. What would you do? E.J.G.
A. First of all, thanks for the background and amount of information. It certainly helps to understand your study and your concerns. However, you did not tell me what type of coating line each of the vendors is using. For the purpose of discussion, I will assume they are each using a square transfer type coating line.
So often when projects like the one you describe are evaluated, they are analyzed solely on the basis of price and fixture cost. If you are not figuring the processing loss into your equation then you should. You also need to be sure you include transportation and logistics cost as well as the potential cost of quality.
If you look at your standard cost of the raw piece part and calculate the average cost of the processing loss you might be surprised at how much of that 17% differential vaporizes. Also, if some of the parts are delivered to your Tier One customer or even the OEM that are not fully coated or not coated at all you could be facing substantial sorting and inspection costs. In addition, there will be an unquantifiable credibility cost because of the blemish this situation places on your quality reputation. These considerations could have a big bearing on the profitability of this project and on your future business with that customer.
Let’s look at some of the possible causes for those pricing and fixture charge differences. Vendor A is using a “universal fixture.” Their charge is probably just to cover some of the maintenance and replacement costs which are shared with other projects using those same fixtures. The term “universal” indicates to me that these fixtures are used over a wide range of part configurations. This type of racking fixture is less expensive to make, store, retrieve and maintain.
Universal fixtures are generally good for heavier parts that will make good contact with the racking fixture. They can also withstand more turbulence in the paint bath. However, your part sounds like it has a high surface to weight ratio. Therefore, it is going to be more subject to being carried off the rack in the E-coat bath and that can cause your processing loss. These racks are probably being used to coat other part configurations that do not hang on the same on the hook. That means the hook on the rack will get more coating on it. Since your parts are light, they are probably not generating enough contact to allow a consistent electro-deposition of the normal amount of paint.
The “adjustable fixture” used by Vendor B will allow the rungs of the rack to be re-positioned up or down the frame to accommodate different sizes of parts. This helps the operator load the number of parts on the rack that will more closely optimize the amount of paint that can be deposited on the part in the time allowed by the system. Since these racks are designed to be used for coating several part configurations as well and they have most of the same contact issues and coverage problems as the “universal fixture” concept has.
You say that “specifically designed fixtures” are being quoted by Vendor C. Many coating companies do not like to use this concept because of the design techniques required and because of the fixture storage and retrieval requirements. However, in my opinion, this is the best fixture concept for small parts like yours.
Here’s why. The racks can be designed to secure the part on the rack so it can resist the current of the paint in the paint bath. Other issues, such as drainage and control of air pockets, can also be addressed with the rack design. The position of the part on the rack will always be the same and this will assure consistent electrical contact for coating deposition. A paint bath will have an optimum substrate surface area that can be correctly coated within the standard immersion cycle. That is, the fixture can be designed to contain the proper number of parts for optimum coating deposition and thickness. There could be a little more labor involved in loading and unloading, but that will not always be the case and in some cases there could be less labor.
This is a long answer to a long question. If there was a short answer, it might be that you should look at the coating system and the racking system that the vendor will use to coat your parts. If the system is obviously designed to favor large parts then you may not want to have your small, lightweight parts coated there. On the other hand, if the vendor’s equipment and racking systems are designed to accommodate small parts you may not find them to be competitive for larger parts like those over two square feet in area. I hope this information helps..
Question: I am responding to the article in the January 2001 issue regarding the comparison between powder coat and electrocoat performance.
This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2012 in Las Vegas, Nev., on June 12, 2012.
How do you measure the surface area of a threaded fastener? How much coating would you put on it? How thick of a coating? What about non-threaded fasteners? The U.S. Department of Agriculture’s Forest Service, of all people, may have come up with the solution for those pondering how to coat sometimes-difficult small pieces using computer imaging and software to compute the area.