- October 23, 2011
- Case Study
To manufacture near perfect flatness (0.001 in) and parallelism (0.0004 in) in its vises, Kurt uses its own gaging and workholoding systems. Both control the variables that occur in the machining, heat treating and grinding operations
October 23, 2011 - Kurt is known for its vises – known for the accuracy and ruggedness these time-proven workholding gems have delivered for more than 50 years. Accuracy is what Kurt vises are all about. To manufacture near perfect vise level flatness (0.001 in) and parallelism (0.0004 in) in its vises, 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 the world-famous Anglock vise. This article describes the automated gaging and workholding Kurt designed into its APS to control all functions and deliver a quality product. Insights into how the gaging controls the grinding operations reveals why Kurt experts design the very best products and then use them to their advantage to make their own products even better. The APS cell setup consists of four horizontal machining centers equipped with five machining pallets to hold the vise bodies for machining. Each pallet can serve any one of the machining centers 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. Many Machines With Many Operations Multiplies The Chances For Error “The challenge for achieving repeatable accuracy with this multi-capable system is that any given vise 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 vise body can be machined on one of four horizontal machining centers, utilizing one of five machining pallets. That same vise 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 gaging station that monitors each process (machining, heat treat and grinding) after each process is completed. Without changeover, the gage station quickly measures a family of vise bodies through each operation, monitoring and controlling the entire production process from the raw cast vise body through final finish grinding. “When a vise 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 gage provides measurement data over the entire length of the vise body so the system operators understand exactly what the part’s measurements are before and after each operation,” Mr. Lenz stated. Proven Software Of Kurt’s Design Provides A “Leg-Up” For Achieving Successful Gaging The SPC software guiding the APS is Kurt’s own, highly refined KurtSPC Premium and Manager software. It provides fully automated machine and CNC control and automatic data collection interactions. There are many features of this software but the most significant is its time-proven use by thousands of manufacturers spanning key industries including vehicles and beverages. Applications include gaging for the manufacture of pistons, truck wheel rims, axels and beverage cans, many of these are for Fortune 500 users. 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. System Software Controls Grinding Operations Utilizing DockLock Workholding System The two Chevalier Smart B246011 CNC surface grinders in the APS process up to sixty different vise 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 vise bodies securely for grinding. The positioning and locking process takes just seconds with repeatable accuracy. (Photo Five) The receiver plate set-up on both grinders accepts up to three pallets at one time depending on the size of the vise bodies and the operation required. Once the pallets are loaded by the robot onto the grind bed and positioned with DockLock locators, a gage measuring head is automatically brought into position to verify location of each pallet and the height of each vise 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 vise 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. The gage 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 gage 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 gage head is set to verify the finished process accuracies. (For gage accuracy and mastering purposes, a fixed pin independent of the grinder pallet is used to verify and master the gage 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. Data Collection And Analyzation Improves System Process And 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 Mr. 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 center, each grinder and so on.” “Our gaging 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 vise 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.” Automated Gaging Replaces Trained Operators Prior to the APS system installation, Kurt manufactured its vises using traditional heat treating, machining and grinding cells. Gaging to Kurt’s high standards for quality was done by trained operators. “Gaging was a slow process,” reports Jon Baller, software development manager for Kurt Engineered Systems Group. Previously done by trained operators, the gaging 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 labor. 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 vise 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.”Learn More
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