November/December 2019

INTEGRATED SYSTEMS 46 HYDRAULICS & PNEUMATICS November/December 2019 www.hpmag.co.uk establish our target position to +/- .0005in.,” said Shindledecker. Gasbarre has been using controllers from Delta Computer Systems, Inc. of Battle Ground, Washington for fifteen years. “We started with the RMC100 and migrated to the RMC150,” said Shindledecker. “When we needed more axes than we could fit into the eight-axis RMC150, we switched to the RMC200, which can handle up to 32 axes.” A strength of the RMC200 (Figure 3) is the ability to connect to a large number of input transducers. In the case of the new Gasbarre press design, the motion controller connects directly to 17 high- precision pressure transducers and seven linear position transducers with SSI (synchronous serial interfaces) and .5 micron resolution. It also connects to one rotary SSI transducer and one load cell. Sixteen of the pressure transducers are paired one on either side of the piston in each of the eight cylinders to measure the force that is being applied (the difference between the pressure readings corresponds to that cylinder’s force). “In addition to measuring force, we are monitoring pressures for diagnostics,” said Shindledecker. “The Delta controller makes a great tool for troubleshooting when everything can be recorded and graphed together.” “With the added monitoring we will have more data available to assist in future upgrades and better utilisation,” adds Heath Jenkins, president of press and automation business at Gasbarre. Besides the pressure transducers, the upper cylinder is fitted with a load cell for the purpose of reading the compaction force that it delivers. Gasbarre’s experience is that the load cell provides more accurate force readings than using pressure transducers in cylinders, without needing to worry about external influences like seal friction. Programming the motion The motion programming and tuning was done using Delta’s RMCTools interface. The software uses drop-down menus and fill-in boxes on screen to program the motion sequence for each axis. “The Delta synchronisation commands are straightforward and easy to work with,” said Shindledecker. “Most of the other motion controllers I have used are less intuitive.” For example, developers can work directly with gear ratios, timing and rates of A sample machine cycle The typical compression cycle is composed of three basic steps: fill, mold, and eject. Each of these have several options under motion control by the Delta Computer Systems RMC200. 1. Fill a. Suction Fill i. The filler shoe moves in over the die cavity while all the punches are in the down position. ii. The die table, lower #1, lower #2, lower #3, and core rod move up to their fill position. This would be a synchronised move. They will all have a different fill position and they all need to arrive at the same time. iii. The filler shoe oscillates back and forth approximately .75” (user programmable) while the lower punches are moving to their fill positions. This is to ensure a complete filling of the die opening. iv. The filler shoe will begin to retract and the die table will move down approximately .040” (user programmable) as a geared move with the filler shoe. This is used to control the front to back distribution of the material within the die. v. The die table moves up approximately .100” (user programmable). This is used to put an air gap between the top of the material and the top of the die table. This is to control any material splash out when the upper punches enter the die cavity. b. Gravity Fill - Similar process with the exception that the lower punches move to the fill position before the filler shoe moves into deposit material into the die cavity. 2. Mold a. While the die table is moving up at the end of fill the upper #2 is moved to its fill position and the upper ram begins to move down. b. When the upper ram is approximately .375” (user programmable) above the die table the traverse speed of the upper ram is decreased to allow the upper punch to enter the die at a slower velocity. c. The upper ram will enter the die a programmable amount and stop. A delay can be used at this point to allow any trapped air to escape before compaction begins. d. All punches begin to move to their mold position. This is done as individual cammed moves to a virtual axis. This is to better utilize the torque curve of the pump. At the beginning of compaction the force required is low and the flow required is high. To make more efficient use of the pump motor, the compaction speed is lowered as the force load increases. e. A dwell at pressure can be set at this point. f. The punches are moved programmable distances to decompress the part and compensate for any punch deflections. g. A dwell can be set at this point. 3. Eject a. The die table will begin to move down for ejection. b. When the die table reaches the next highest punch level that level begins to move with it. c. When they reach the next level it begins to move with it. Until all the lower punches are in the eject position. d. The upper ram will move up to its retract position. e. End of cycle – Total cycle time depends until cylinder travels but will be between 6 and 14 cycles per minute. Figure 2. A sample part produced by Gasbarre’s new powder compacting press.