When you think of something that will withstand temperatures of up to 5,500 degrees, tape probably doesn't enter your mind. But, particularly in the aerospace and defense industries, tape comes into play. One popular method of converting high-tech, composite, thermal-setting materials into super-tough, durable three-dimensional products is tape-wrapping. It is an alternative to manufacturing methods such as molding (i.e. injection, compression, isostatic) and lamination. The need for this alternative process came about as rocket motor sizes increased. As tape-wrapping commenced, it was also found that it offered significantly superior erosion resistance. For tape-wrapping machines, the thermoplastics used are supplied to the manufacturer in rolls of "tape". The supplier has woven tapes from continuous filaments embedded in polymer, combined with heat-activated epoxy. Reinforcement of the composite material occurs by carbonizing or graphitizing the filaments prior to the weaving process.

Edler Industries of Newport, California, transformed a 50-year-old lathe into a new tape-wrapping machine, incorporating a tightly controlled closed loop process utilizing the newer AC drive technologies, automated multiple axis-control, programmable logic controllers and closed-loop, automated regulation of flow, pressure and heat. Edler manufactures composite materials used in aerospace and defense industries.

While the materials used for tape-wrapping have made great technological advancements, the machines used to do the wrapping have remained relatively low-tech. Methods used during the manufacturing process for controlling variables that are critical to the process (i.e. speed, positioning, heat and pressure) have been loosely applied.

Edler Industries of Newport, California is developing a new machine that features a tightly controlled closed loop process. Using several Siemens Energy & Automation products as a total solution, the machine and process control sets a new standard for composite materials manufacturing, and gives the customers a new level of confidence for the final products.

Tape-wrapping of thermoplastic materials is an alternative to other manufacturing methods such as molding (i.e. injection, compression, isostatic), and lamination. The need for this alternative process came about as rocket motor sizes increased. Woven tapes have continuous filaments embedded in polymer and combined with heat-activated epoxy. The composite material is usually reinforced by carbonizing or graphitizing the filaments prior to the weaving process.

The Right Opportunity Presents Itself In early 1999, Edler purchased a large lathe and modified it to double as a tape-wrapping machine for less than $200,000. The lathe's large AC spindle motor was re-wound to accommodate an AC drive and modified from 1800 rpm to 1200 rpm so that it matched the specifications of a 40hp SIMOVERT(r) VC vector-controlled electronic drive (6SE70) from Siemens. It included a dynamic brake option. Edler chose an AC vector drive over the conventional DC drive solution because of the wider speed regulation range, lower cost and maintenance issues. The gearbox for the spindle has a wide range of ratios that are managed by a mechanical clutch on the gearbox. The typical tape-wrapping operating speed of the spindle is regulated between 1 and 60 rpm, depending on the size of the shape wound and nature of the winding material used.

The wide range of rotational speeds and regulation is beneficial for several reasons. One big benefit is the manufacturing flexibility that it offers. Although most of the wrapping jobs are performed at the low rotational speeds, future products might demand much faster speeds. The same machine can do both. Secondly, since machining is a natural part of the total process, Edler is currently examining the possibility of allowing the machine not only to perform tape-wrapping, but also operate as a lathe to machine the various accompanying metal parts and products to required tolerances. This is an easy conversion.

The existing AC spindle motor on Edler's tape-wrapping machine was re-wound to accommodate this AC drive and modified from 1800 rpm to 1200 rpm so that it matched the drives specifications and could include a dynamic brake option. Edler had chosen to use an AC vector drive over the conventional DC drive solution because of the wider speed regulation range, lower cost and maintenance issues. The gearbox for the spindle has a wide range of ratios. It has a mechanical clutch on the gearbox that provides many ranges of rotational speeds. The typical tape-wrapping operating speed of the spindle is regulated between 1 and 60 rpm, depending on the size of the shape being wound and nature of the winding material being used.

Multiple Axis Control A tape-wrapping machine usually requires adjustment capability for at least three axes - horizontal, vertical movement of the table and application head, and the rotational axis of the spindle\mandrel. It is also beneficial to be able to provide an angular adjustment that allows a "tilting" of the application head. This would require a fourth axis. Currently, the Edler prototype only uses three axes. However, the system's PLC (an S7-300 from Siemens) is equipped with a FIN357 rack-mounted four-axis control module to allow expansion in head mobility capabilities. The horizontal and vertical axes (X-Y axes) are controlled by two 2hp MICROMASTER(r) drives (6SE32) from Siemens. The horizontal table movement provides up to 100 inches between the spindle and the application heads. This provides a large amount of flexibility for adding and removing mandrels of various sizes and shapes. The table can be moved back out of the way very rapidly for product changes and setup because of the responsiveness inherent in the small AC vector drives.

Drive and PLC Considerations While shopping for drives, the development team at Edler viewed several options. A large investment in a drive with plenty of I/O and intelligence was feasible, but an analysis showed clearly that the job could be done cheaper and better by combining the drives with a PLC to handle the I/O requirements and give the corresponding drive commands. Standard old-style tape-wrapping machines usually do not include a PLC, but the new machine has over 100 I/O points that come into the picture. This is a routine capability for the S7-300 PLC equipped with a Profibus(r) module for rapid communication capability and open protocol. All three of the drive motors were equipped with pulse tachometers for feeding actual speed data for comparison to the set points that have been stored in the drives' memory. Because of the gearbox arrangement, an encoder is not required for the spindle motor to provide the kind of wide speed range capability the system offers.

Edler's tape-wrapping machine requires adjustment capability for three axes-horizontal, vertical movement of the table and application head, and the rotational axis of the spindle\mandrel. It is also beneficial to be able to provide an angular adjustment that allows a "tilting" of the application head, requiring a fourth axis. The system's PLC is equipped with a rack-mounted 4-axis control module to allow expansion in head mobility capabilities.

The three drives from Siemens are also very small compared to the DC drives used on the older tape-wrapping machines. In fact, all three drives fit into a wall-mounted cabinet that is barely 4'x2' in size. This is not much bigger than half the size of the DC drive cabinets that were being used on Edler's older machines.

Heat, Pressure and Flow Control
Careful attention was given to the heat sensing and control for the new machine. Enough insulation in the ductwork makes sure it is more resistant to the ambient outside temperature changes and the PLC controls various elements of the heat supply system. Adjustment of both flow and temperature is PLC controlled automatically against programmed set points via a closed proportional control loop.

Pressure is applied by pneumatically-controlled roller plates. The pressure is measured against a set point by the PLC via data reported by pressure sensors. Automatic adjustments are made by the PLC to keep the pressure uniform and within the proper range.

Uniform cooling of the tape-wrapping process is also important. Carbon dioxide is used to cool the rollers so that they do not stick to the tape, and it is also used to cool the tape as the consolidation process is completed. The PLC regulates the proper timing and heat measurement that is essential to this process.

Human Machine Interface
Monitoring and override capability is provided via a OP27 touch screen display from Siemens. The software used for monitoring, alarm reporting, data logging, and real-time machine adjustments is the standard STEP 7 ProTool, designed for use with Siemens Plus.

Conclusions
The new machine is still being upgraded continuously due to the flexibility provided by the PLC concept, yet remains in full production use at Edler. It took two individuals less than six months to modify the lathe, add the control equipment, do the testing, and commission it for full operation. Because so much of the machine work is performed automatically, less is required of the personnel who operate it. Edler Industries now has plans to eventually upgrade all of its other tape-wrapping machines to this newer technology and process design.

Product Information: Drives Solutions