QMT Features: November 2011
Clamp down on accuracies
Gauging ensures 0.001 inch flatness and 0.0004 inch parallelism while controlling dozens of production variables In an automated production system for manufacturing workholding vices.

Minneapolis-based Kurt is known for its workholding vices and accuracy is what Kurt vices are all about. To manufacture near perfect vice level flatness (0.001 in) and parallelism (0.0004 in) in its vices, two lesser known but extremely important Kurt products are used in its Automated Production System (APS): Kurt Gaging and Kurt Custom Engineered Workholding. Both control the variables that occur in the APS’s machining, heat treating and grinding operations as the system processes 8 different models and sizes of itss Anglock vice.

The APS cell setup consists of four horizontal machining centres equipped with five machining pallets to hold the vice bodies for machining. Each pallet can serve any one of the machining centres tended by a Fanuc robot which provides all of the load/unload functions throughout the cell. Following machining, heat-treating is done in another machine equipped with two heat treat stations. Grinding is done in one of two grinders, each of which has three grind positions and is served by six grind pallets. (Photo 2)

“The challenge for achieving repeatable accuracy with this multi-capable system is that any given vice body can be processed through a very large number of production possibilities,” reports Jeff Lenz, division manager of Kurt Industrial Products/Engineered Systems. “For example, a particular model vice body can be machined on one of four horizontal machining centres, utilizing one of five machining pallets. That same vice can be heat treated in one of two stations. Grinding can take place at one of six grind stations on any one of six pallets. With this multitude of possible production scenarios, we accomplished our objective of flatness (0.001) and parallelism (0.0004) using Kurt’s custom gaging, workholding and SPC software.”

To control all of these production scenarios, Kurt designed and built a gauging station that monitors each process (machining, heat treat and grinding) after each process is completed. Without changeover, the gauge station quickly measures a family of vice bodies through each operation, monitoring and controlling the entire production process from the raw cast vice body through final finish grinding.

“When a vice body is loaded into the fixture, a series of LVDT probes measures the part for flatness, thickness and parallelism. This takes about 30 seconds. The gauge provides measurement data over the entire length of the vice body so the system operators understand exactly what the part’s measurements are before and after each operation,” Jeff  Lenz stated.

SPC and gauging
The SPC software guiding the APS is Kurt’s own, KurtSPC Premium and Manager software. It provides fully automated machine and CNC control and automatic data collection interactions.

Examining the grinding process shows how well the software manages the grinding process, how it interacts with the other steps in the APS cell and how it delivers a high level of consistent quality. (Photos 3 and 4)

The two Chevalier Smart B246011 CNC surface grinders in the APS process up to sixty different vice configurations. To accurately position and hold all of these different sizes for grinding, pallets are equipped with Kurt’s DockLock, a pneumatic positioning system that is anchored to each pallet. The bottom of each pallet has four zero-point locating pins that are actuated by springs to position and retain them and air to release them. The pins locate accurately within 0.0002 inch enabling the DockLock’s pneumatic cylinder to lock vice bodies securely for grinding. The positioning and locking process takes seconds with repeatable accuracy. (Photo 5).

The receiver plate set-up on both grinders accepts up to three pallets at one time depending on the size of the vice bodies and the operation required.
Once the pallets are loaded by the robot onto the grind bed and positioned with DockLock locators, a gauge measuring head is automatically brought into position to verify location of each pallet and the height of each vice body. This is accomplished by electronically measuring the height of the rest pins on the pallets four corners.

This verifies that the pallet is aligned to the table bed, and equally important, tests for any load problems. Height verification determines the amount of grind needed for each vice body. If the height and load is not correct, the robot will try to reposition the pallet. If unsuccessful, the pallet is removed and simultaneously triggers an alert to the system operator for follow-up action. (Photo 6)

The gauge measuring head is designed to withstand the harsh grinding environment. Coolant and slurry action has no effect on the gaging operation or its accuracy. Communication between grinder and gage is done utilizing the KurtSPC data collection software and KurtUSB direct gauge interface hardware. The part measurement data with grind start/stop dimensions are communicated directly to the grinder controller. When each grind cycle is completed, the gauge head is set to verify the finished process accuracies. (For gauge accuracy and mastering purposes, a fixed pin independent of the grinder pallet is used to verify and master the gauge at predetermined and programmable cycles.)

By controlling the grinding using KurtSPC, this process step alone experiences a 30 percent reduction in cycle time. That doesn’t include the reduction of waiting time required with the old manual load/unload operations.

Process consistency
“By collecting data through weeks of start-up trial and error to understand and address all of the variables in the process, we were able to identify problem areas and continually improve the process, eliminating variation caused by fixtures, tooling and other issues,” reports Jeff Lenz. “When we started collecting data in one large population, we generated a distribution that had several modes suggesting that there was more than one process in the data. The data showed, for example, the signature of each horizontal machining centre, each grinder and so on.

Our gauging setup assures us that regardless of the combination of machine tools, fixtures and tooling within the APS cell, we are able to produce very consistent vice bodies. When problems arise – and even more beneficial – when we develop changes in tooling, fixtures and feeds on a machine to optimize the process even more, we can easily analyze the impact on our production. That’s a good thing.”

Replaces Trained Operators
Prior to the APS system installation,  Kurt manufactured its vices using traditional heat treating, machining and grinding cells. Gauging to Kurt’s high standards for quality was done by trained operators.

“Gauging was a slow process,” reports Jon Baller, software development manager for Kurt Engineered Systems Group. ” Previously done by trained operators, the gauging process was held to Kurt’s high standards for precision but was subject to human variation from one operator to another and from one production shift to another. Keeping quality consistently high was a challenge. When we designed the new APS, the goal was to monitor accuracy electronically in real time with traceability of each process step. We accomplished that plus we make more effective use of our labour. With the new APS, we only need three operators where with the old system we needed five. Also, the new system ramps up easily as we experience more variation in the order mix and increased order size.

There are a lot of advantages to this system.  One of the most significant was to design and implement a large-scale system within our own vice manufacturing giving us a chance to really show off our capabilities. It gave us the tools needed to maintain the highest quality to compete in the global market.” l
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