Gears are hard to make. They come in all shapes and sizes and are made out of a variety of materials. Our customers dream up these things that cause nightmares for the faint of heart.
So, let’s start at the beginning when we generally get our first look at the print—quoting. You open the email and begin the journey to make the product. What do you look for first? Second? Third? Looking for the trash can yet? Just kidding.
Since you’ve already decided what types of products you want to quote, (we’ll discuss this in more detail in future columns), the first issue is whether or not this fits your criteria and if it’s the kind of work you want to take on. If so, move to step two. If not, no quote and move on to the next RFQ.
Assuming that you want to quote, what’s next? I usually look at a number of items, not necessarily in this order:
• Heat Treatment (if required)
• Customer Quality requirements (documentation)
I’m sure most of you do the same thing and start creating a routing in your head based on what you’ve found. It’s basic, but if you don’t look for these things, you could wind up with a real loser. I’m sure many of you have seen prints that look like they came off of a napkin with nothing more than a generic material like “steel” and the number of teeth they want and with no diametral pitch or pressure angle, either.
Assuming you’ve gotten something a little more specific, the next step for me would be to look at how the material and heat treatment will interact to make the parts harder to make. Configuration also comes into play with such nuances like selective area heat treatment, thin sections and hard to get to dimensions that are also close tolerance.
Heat treatment is probably the biggest headache you’ll have with any gear. Gears are hardened to make them stronger, but let’s think about this. After you’ve put a ton of time and effort into making a good gear, the heat-treater sticks the parts in a furnace, heats them up to some temperature and then quenches them quickly usually in oil. In carburizing and nitirding, carbon and nitrogen are circulating in the atmosphere and soak into the material. Shocking, right?
This rather traumatic treatment forces the gear manufacturer to process those parts around what he believes the parts will do in heat treatment—grow, shrink, go out of round or all of them at the same time. Experience will guide you, but sometimes things happen, and the parts are scrap. You’ve got to build that in, too.
I know what you’re thinking. The customer just doesn’t get it. Or, they don’t care. They just want the part to the print. It’s up to you to educate them as to why putting difficult or even ridiculous specifications on prints causes high prices. But, I digress.
Once you’ve gotten past the heat treat aspects, tolerances are probably next. When I see decimal points with lots of zeros followed by numbers, I get nervous. If you see a lot of .0005 inches or smaller tolerances, chances are these parts are going to be tough parts to make. It isn’t that they can’t be made, just that the job will be tougher.
Some to be weary of are those that will be affected by heat treatment are those that are tight to make before hardening and can’t be or are difficult to re-machine after hardening. Blind hole keyways and splines, cluster gears, thin sections, and small radiuses come to mind.
Customer quality requirements can also drive you bonkers if they are looking for inspection reports on parts that will have you do a process after final inspection including shot peening and the removal of extensions/centers from the parts that were used to manufacture the parts. If you’re going to prove you made the parts to the print, you will have to inspect them before these processes are done. If you’ve got to provide lots of documentation such as SPC data, PPAP, or special process documents, these requirements must be a part of your routing and ultimately your cost to sell the parts.
Even the quantity can affect your process. If you are quoting a large quantity, you might figure in buying that special cutter for the parts. For a small quantity, maybe not. Some quantities would require an automated machine while others use manual loading. It’s just a matter of how much effort you want to put into the parts to get the end result.
Delivery is always an issue depending on how quickly the customer wants the parts versus the time required inside the shop plus the time to send the parts out for any processes you can’t do. If it takes too long, no one is satisfied. Customer communication is the key, and some negotiation may be required to get to a date everybody is happy with.
These are the basic concepts that most manufacturers look at to develop their routings. Whatever the situation, you’ve got to take the time to review all the information and then plan out the operations. The good news is that as you gain experience, this task will be easier even with complex parts. As the saying goes, “You can’t make a silk purse out of a sow’s ear.”