Like any industry, in the machine-tool industry, the needs of the market drive new designs and the development of new technologies. Naturally, everyone wants machines to be less expensive to operate, to require less maintenance, and to be easier and safer to operate. They want a machine to take up less floor space and to produce higher quality parts. Broaching Machine Specialties (BMS) has developed a solution: the BMS Dual-Drive broaching machine.
The BMS Dual-Drive is an electromechanically powered, table-up vertical broaching machine for all types of internal broaching applications. The use of electromechanical drive technology is not new to BMS. The company has been building its Electro-Mate, electric drive table-up broaching machines since 1994 (Figure 1); however, the design of the machine has evolved from a single screw, “slide-and-way” construction to a dual screw H-Frame construction (Figure 2).
While this type of broaching machine design is not prevalent in the U.S., it has been in widespread use in Europe and Asia for decades. A major advantage of the H-Frame design is that it yields better part quality than can be achieved using the traditional, North American, slide-and-way type design. In slide-and-way construction, the moment created by the broaching force can cause deflection of the work table, resulting in parts with excessive face run-out or issues with perpendicularity.
In the H-Frame construction, the moment arm that can result in degradation of part quality is eliminated. In this construction, the workpiece is on center between the two “prime movers,” and all the broaching forces are in line with the part centerline. Any deflection in the table is directly in line with the tool path, which does not show up as face-runout or problems in perpendicularity (Figure 3). A manufacturing engineer at an American helicopter manufacturing company had this to say about the quality they achieved with the Dual-Drive: “We had been getting 0.005” to 0.006” face run-out in our parts, but with the BMS Dual-Drive, that was reduced to 0.001”. We are actually broaching 10 different part numbers on the machine without any issues.”
Floor space requirements
Like all electric drive broaching machines, absence of a hydraulic unit reduces the required floor space by approximately 50 percent, but with its compact, yet rugged, design, the BMS Dual-Drive reduces the floor space requirements even further. For example, the previous design of BMS’ 15-ton, 60”-stroke electric drive table up machine required approximately 40 square feet of floor space, but, the same capacity Dual-Drive machine requires only 36 square feet of floor space. When compared to a hydraulic machine of the same capacity, floor space savings totals 37 square feet.
The table-up design yields even more floorspace savings because it does not require a pit or operator platform, thereby decreasing the floor space requirements even further and allowing cells to be more easily reconfigured. The floor-loaded design also simplifies part handling because parts are loaded and unloaded at floor level and frees up additional floor space for part dunnage or other production equipment.
The Dual-Drives’ electric drive offers many more advantages including:
Better Part Finish and Tool Life: Powered by planetary roller screw drives, there is virtually no backlash or vibration of the cutting tool in the Dual-Drive machine. In typical broaching operations, the forces change continually throughout the cutting stoke, as the number of cutting teeth engaged in the part varies when the teeth enter and exit the workpiece. In a hydraulic machine, due to the compressibility of hydraulic oil under pressure, the broach tool will vibrate as the cutting forces change. This results in a degradation of part finish and tool life. Tool vibration is virtually eliminated in the Dual-Drive and, depending on the application, tool life can improve as much as 30 percent.
More Comfortable Plant Environment: Because the Dual-Drive has no hydraulics, the machine doesn’t get warmer as it operates. Cooler operation means less heat is dissipated into the plant environment, which results in happier and more productive machine operators.
Consistency and Reliability: The performance of hydraulically powered machines can be affected by the temperature of the hydraulic oil in the reservoir. The response time of the hydraulically powered slides may be different when the oil is cold versus when the oil is warm, causing the operator or set-up technician to have to adjust the stroke limits or cutting speeds. The Dual-Drive operates consistently and reliably, regardless of the time of day, the temperature of the plant, or how long it has been cycling.
Ease of Set-Up: As the machine is powered electrically, both the machine stroke and speed are programmed into the servo drive, and both can be easily changed through the touch of a button, rather than the manual adjustments of limit switches or valves as required in a hydraulically powered machine.
Quieter Operation: Rotating pumps and hydraulic oil coursing through pipes and cylinders make for a loud machine. These “noise makers” are eliminated in the Dual-Drive and noise level limitations are met easily.
Every moving axis of the Dual-Drive is completely enclosed within the machine guarding. The access door is automatic and fully interlocked to the machine cycle, ensuring that the machine cannot cycle in auto mode until the doors are closed and the operator is fully clear of the work area. An additional level of safety is added to the door itself with a safety edge that causes the door to open if there is any obstruction between the two horizontally-sliding panels. (Figure 4)
Safety during tooling changeover was also addressed by BMS. All Dual-Drive machines come complete with a pre-programmed “maintenance” mode accessed through the touch of a button on the HMI. When in maintenance mode, the machine automatically moves into a pre-set position allowing for the broach pullers to be easily accessed for changeover and for other maintenance tasks to be completed under the machine slide. The slide is automatically held in position with a static brake, but redundancy is provided with an insertable, interlocked safety support bar placed under the slide assuring it remains in the “maintenance” position and achieves 100 percent safety when servicing the machine.
Even further safety during maintenance is offered because the safety support bar is stored in a docking station on the machine itself and interlocked with a switch assuring the machine doesn’t operate until the bar is safely returned to storage. (Figure 5)
Ease of maintenance
The Dual-Drive has integrated shed plates directing chips to a central location for efficient removal with a chip conveyor and coolant washes plumbed directly into the bottom of the broach pullers. In less sophisticated broaching machines, keeping the broach pullers free of chips requires regular attention, but the continual washing of the pullers in the Dual-Drive ensures the pullers remain chip-free, resulting in less maintenance and greater machine uptime.
Further reductions in maintenance and downtime are realized through the use of the BMS “Posi-Lock” series of broach pullers and retrievers. Gone are the springs that fatigue and fail resulting in broken and damaged broach tools and machine crashes. The “Posi-Lock” series of pullers and retrievers are pneumatically actuated and electrically interlocked to ensure the broach tools are properly engaged and locked in the pullers and retrievers at the appropriate times during the machine cycle, thus eliminating “dropped,” damaged, and broken tools and machine crashes that can result in damage to the machine.
Not only does the Dual-Drive significantly lower initial capital expenditure costs for new broaching equipment (a new Dual-Drive costs no more than a remanufactured machine of similar capacity), but it significantly reduces the cost of ownership by lowering operating costs. Unlike a hydraulically powered machine in which the electric motor is constantly running — even when the machine is idling, the motors on the Dual-Drive only run when the machine is in motion, which results in an annual electricity savings of approximately 50 percent.
The machine requires no hydraulic oil, so not only is the cost of consumable hydraulic oil eliminated, but the costs incurred for disposing of depleted hydraulic oil is also eliminated.
The cost of maintenance is also reduced, as the machine has fewer moving parts than a hydraulically powered machine. The Dual-Drive has no hydraulic valves, pumps, pipes, or fittings to maintain, and the auxiliary machine motions are powered either electrically or pneumatically. The result? No leaks to fix and no slippery floors to clean.