Setting Up In-process Gaging
In-process gaging allows a manufacturer to get control of its process and ensures that every part is good, thereby eliminating scrap. If parts are measured post-process instead of in-process, by the time a part is taken off a machine and inspected, parts are either good or bad and the outcome cannot be changed. With in-process gaging, by taking control of the process, it ensures every part is going to meet specifications.
To get the best measurements and best parts possible, in-process gaging needs to be user friendly, repeatable and reliable, and remove operator influence.
In order to make a gage operator-friendly, the gage builder has to know what the customer wants to measure. With in-process gaging, a dimension such as process-sensitive or critical dimensions are picked. This is usually the overall length because the longer the part, the more sensitive it is to change, says Richard Caya, president of Alliance Gaging Solutions, a Division of Alliance Mold & Machine Inc. (Pascoag, RI).
Caya says a gage builder must build a personal rapport with its customers. This rapport helps when it comes to designing operator friendly gaging systems. After talking to engineers and inspectors, Caya shows them a sketch of what he thinks will work for the project. Optimally, the engineers and inspectors will give their feedback and throw out some ideas. "That makes it nice because if it works as well as they envision, they're going to be happy with that gage," he says.
Caya says if operators are not happy with the gage, they will work to find ways to do their jobs without having to use the gages. Caya is currently working with a company that asked him to modify some tools built by another company because the operators do not like using them. "The operators have gone back to measuring the parts one at a time on a CMM (coordinate measuring machine) rather than use the automated system because it just doesn't have the repeatability or because it is so hard to load the parts into that people just don't like using them. They can put the stuff on a CMM and come up with the numbers as quick as they can between loading and using these fixtures. They'll find ways around it."
Dave Hayes, sales and marketing manager for Control Gaging Inc. (Ann Arbor, MI) also says his projects start with the engineers because they are able to define the project and its parameters. "We have to find out what they're trying to accomplish and the reasons they're trying to do it because we have different equipment we can supply." If the biggest concern is extremely fast setup time or no setup at all, and the gage does not need to be extremely accurate, one type of setup is supplied. But if a customer needs the gaging as accurate possible and is not as concerned with setup time, then another method is supplied.
Control Gaging's philosophy has always been to keep gaging as easy as possible, according to Hayes. The company makes quick setup products that reduce the amount of decisions the operator has to make by limiting the number of buttons to push. Hayes says less is better and his company focuses on providing the operator a way to do a process in the fastest amount of time and with the least amount of training.
While the industry trend seems to lean toward simplicity to accommodate the skill levels of all operators, Hayes says that many younger workers appear to prefer more complicated systems and they learn them much faster than older workers. "But you're asking operators with all of this computerized equipment to learn many different interfaces and many different ways to set up different pieces of equipment. And our goal is to keep our equipment simple," he says.
One way to keep an operation simple is to remove operator influence where possible. Most of the fixtures Caya builds have statistical process control (SPC) output capability. One of his customers is fully automated and does not want employees to write down any data. The customer wants the gage to put out a number, have the operator hit a button and have the data go directly to a computer, thereby eliminating manual input and the possibility of human error such as transposing numbers or changing input. "When you rely on someone entering numbers, there is always a chance that they might make a mistake. With SPC, it's in there. It can't be changed easily. It's all automated," he says.
Removing operator influence also allows the operator to run multiple machines. Hayes says that with the United States facing global competition and having among the highest labor rates in the world, if an operator can run more than one operation, the cost per part is reduced.
Repeatability and reliability
In-process gages are comparative gages, not absolute gages. Because of that, Hayes says the gages are being graded on how well they repeat. "In other words, when you're measuring a part with an in-process gage, the gage doesn't necessarily know if it's 1 inch or if it's 6 inches. It just knows what the final size should be and that every part should match identically to that size, so repeatability is the key."
Caya says good gage repeatability is a must on the fixture because if all of the tolerance budget is used up on the gage, accuracy is lost. "Most of the time I shoot for less than 10% for gage repeatability. In the industry, up to this point, most places will settle for up to 25%. I don't like that because you lose a lot of the room that the customer has to process within," Caya replies.
Not only is repeatability key but so is reliability. "When gaging is moved to in-process and you stop relying on checking every single part post-process, that gage has to work and it has to keep working. If it goes down, it's going to cost a lot of money for downtime," says Hayes.
A large part of Control Gaging's business is bearings customers. Hayes says that should a machine go down for any reason, the company is losing more than $1,000 per hour in lost production. "So reliability becomes a key, especially with just-in-time inventories," adds Hayes. "You can't afford to shut something down because a component failed."
Time is money
In addition to keeping the process in control and reducing scrap, in-process gaging has other advantages. Time is saved because an operator does not need to check every part after it is produced because by using in-process gaging, every part is controlled to the correct size while it is being machined.
Hayes adds that often with in-process gaging, the metal removal rates on the machine can be sped up. "When running a machine without a gage, every single cycle has to be repeatable and that's difficult because the parts coming into the process often have different amounts of stock, so the machine has to run a little bit slower to account for the variation of the incoming stock. When you run with an in-process gage you can go much faster because the effect of the differences in incoming stock is greatly reduced."
While the cost of in-process gaging may be more expensive than other types of gaging, Hayes says that it outweighs the risk of getting a bad part in the product stream.
Sidebar: Tech tips
1. To make a gage operate efficiently, the gage builder needs to know what the customer wants to measure.
2. In-process gages are graded on how well they repeat.
3. Removing operator influence helps control quality.