Higher flexibility in the machining center
Keyword: “The dedicated machine cycle time must be shorter, but when it fails, it can only be restarted after the machine has been repaired. If you want to reconfigure the tool for a special machine for another batch of machining tasks, then This money can almost buy a new, more flexible CNC machine that is more suitable for today's production requirements." If you feel that the special machine is coming from the Visteon chassis (in Indianapolis, Indiana) The factory exits, then your feelings are right.
The chassis manufacturer specializes in the production of power-assisted rack and pinion steering mechanisms for passenger cars and trucks, and has eliminated about half of the indexing machines used to produce the input shaft, a key component of the power steering valve. When the input shaft workpieces machined on the remaining indexing machine end or change, the plant plans to decommission them without reconfiguring them.
The input shaft is a cylindrical steel part approximately 6 inches long and 1 inch in diameter, machined from the bar stock. It requires a large number of processes, including the "Op 80", in which a large number of holes (hydraulic fluid passages) are drilled through the outer diameter of the main bore running through the length of the part.
Small things are sometimes important. One of the main reasons for choosing this machining center is that it can be drilled at high speed, which is a prerequisite for successful drilling of the hole (1.5 mm diameter). The governor spindle head in which the drill bit is mounted can rotate up to 20,000 rpm.
Once the input valve was almost completely drilled on the automatic indexing machine. But recently the Visteon plant received a new rack and pinion steering mechanism order where the input shaft required an unusually small hole (1.5 mm diameter). At a meeting to discuss new workpieces, the drill supplier suggested that the holes should be drilled at a higher speed than allowed by the indexing machine, so participants began to consider alternative ways to machine the holes.
Wahid Kapadia, a member of the Pioneer Model Engineering Department, said: "We have a large number of dedicated machine tools in our factory. We are increasingly aware that the time and money spent on adjusting the machine for different workpieces greatly limits the efficiency and flexibility of the plant. For a variety of reasons, we started looking for a CNC machine with a small hole. First of all, many CNC machines have the spindle speed we need to drill the hole. Secondly, it is easy to cut the hole and CNC machine. There are tool control devices that can reduce this problem.
He continued: "Secondly, we want to maintain a high production speed. When a problem occurs with a special machine, production will stop and production will not be possible until the problem is solved. On the contrary, when production is started on several standard CNC machines. If there is a problem with one machine, other machines can continue to machine the parts. Although the production is affected, it has not stopped completely."
The factory initially considered a CNC lathe with powered tools. However, it was unable to find a machine that could provide the required drilling speed for machining small holes.
The factory then inspected the standard CNC drilling and tapping machine. In order to meet the production batch involved, several such machines are required. However, since the machine will be largely unattended, it is necessary to add something else necessary to the relevant workpieces. In order to automate part handling, one or more robots are required. In order to drill the input shaft in 90 degree increments, an indexing clamp is also required. The prospect of purchasing machine tools and configuring them with the necessary workpiece handling equipment for workpiece machining becomes disappointing. So you need to find a simpler solution.
After more research, the factory investigated the A-Series machining centers produced by Wasino, Inc. (Rolling Meadows, Ill.). The A series consists of four-axis (X, Y, Z and C) machining centers with auxiliary turning functions. The series is more like an automatic lathe than a normal machining center. It has a horizontal spindle with a speed of 4000 r/min and a C-axis that can be programmed in 0.0001 inch increments. The main shaft is supplied by a turret, and each of the turrets is equipped with a rotary or turning tool.
The A-Series machines are also equipped with a comprehensive gantry loader that takes the part to be machined from a compact disc-shaped assembly area located behind the machine and returns the machined part to it. The machine has a part handling chuck with a maximum of 10 inches (for the largest part of the workpiece) and a spindle hole that allows the bar to feed or discharge the bar from the bar feeder.
One of the most important features of the machine for Visteon is that the tool turret can directly drive the rotary tool (without any gears) and accelerate to 10,000 r/min, ensuring the required speed for drilling new input shaft holes. Therefore, the factory purchased the A-12 (with 12 turret cutters). To ensure that the plant has a high enough drilling speed for current and future workpieces, it purchased a machine with a governor spindle head that doubled the maximum speed to 20,000 r/min.
Tailored to the part
Mr. Kapadia said: “The main spindle has a C-axis, which can easily meet our needs: the parts are indexed for drilling operations. In addition, the machine's integrated gantry also meets our needs by automatically loading and unloading parts. The spot A-12 can meet our workpiece processing needs in such a complete way that it is tailored to the part."
Initially, the plant plans to continue machining the input shaft on the indexing machine and machine the holes in the CNC machine in a separate process. However, the CNC can drill all the holes and by drilling it, the factory can avoid drilling holes in a separate process. In terms of input shaft drilling, the CNC machine completely replaces the indexing machine.
This scenario is repeated once the factory receives an order for a small tonnage truck-loading power steering mechanism. Initially, it was planned to drill the input shaft of the new workpiece on the indexing machine of the factory. However, further analysis shows that re-equipping a machine tool to machine a new workpiece will incur high costs, and the cost-effectiveness of drilling an input shaft on a new CNC machine is much better. Therefore, the factory purchased three additional A-12 machines for this machining task.
Similarly, the factory purchased a fifth A-12 machine to complete the operation of the old indexing machine that was used to produce repair parts. Two old machines were scrapped. The CNC machine group gives the plant the production flexibility that the indexing machine cannot provide. Mr. Kapadia explained: “All CNC machines are programmed to machine all of our input axes. This means we can machine any part on any machine at any time.â€
These machining centers can also be used to machine temporary workpieces. For example, when the design change of the power steering unit requires shortening the length of the input shaft, the machining center for the repair member is quickly set to perform such a "cut" operation. In addition, when a specific workpiece task needs to be milled on the workpiece, the machining center can be quickly programmed and the corresponding tool can be configured to complete the machining of the workpiece.
An operator looks after five machine tools
At Visteon, the machining centers are arranged in rows. All five machines are looked after by an operator whose main task is to keep the blanks in the discs in the machining center. On the day we visited the plant, most of the machine tools were drilling three different diameter holes in the input shaft: a 7.9mm hole that passed through the flattened body at the end of the part; 8 3mm diameters, every two A hole that is distributed 90 degrees apart from each other along the outer diameter; two holes of 1.5 mm diameter separated by 180 degrees from each other. All holes pass through the main hole in the length of the part. The turret is indexed three times and the appropriate tool is used to machine the input shaft. The total cycle time of the part is 55 seconds.
The factory once used six indexing machines to drill holes in the input shaft. The machining center has replaced three of these machines. The rest of the machine is still in production, but when these parts are machined or the design changes, they will no longer be reconfigured. They will be replaced by more machining centers.
Automatic adjustment of tool offset with the probe on the machining center
When Visteon's Indianapolis chassis plant moved from a dedicated indexing machine to a machining center to drill the input shaft of its power steering unit, the new technology enabled the plant to utilize more advanced cutting tool controls. These CNC machines drill thousands of holes per shift and must be adjusted at any time to compensate for tool wear. The factory does not want its operators to be responsible for these changes. One reason is that an operator operates all five CNC machines and has no time for tool offset compensation. In addition, an error made by the operator may result in a batch of parts that are out of tolerance, or even an accident that cannot be produced by the machine.
This problem was solved after the factory installed a Z-Nano probe on each machining center. Each probe is detected by the probe and automatically signals to the machine controller to compensate for detected tool wear. The Z-Nano probe is manufactured by Blum Ltd. (Erlanger, Kentucky) and has a very sensitive probe (can measure tools as small as 0.02 mm in diameter) and (can be compatible with major CNC controls, A necessary tool positioning change provides an indication of software integration. The repeatability of the probe is 0.001 mm. The measured data is transferred directly from the probe to the machine controller via the protected cable.
In addition to better control of hole size and increased machine operating time, the probe offers the opportunity to save a lot of tooling. The plant uses an integral, TiN-coated carbide drill to drill holes in the input shaft. Mr. Kapadia of Visteon explained: “Before, we have only used new drill bits. One of the reasons is that we don’t want our operators to adjust the offset to compensate for the smaller size of the drill after regrind. Now, because of each machine They all have a probe that can measure the drill bit and automatically make the necessary adjustments, so we have no more obstacles in using the regrind drill bit. The price of a new drill is as high as $50, and the cost of regrind is only a few. One point, so we can save a lot of money."
Mr. Kapadia of Visteon is inspecting an input shaft drilled from five machining centers in the factory.
The lower gripper of the gantry arm has just removed a drilled input shaft from the spindle and is loading a new blank into the spindle (clamped in the upper gripper), which then returns the drilled shaft Go to the output conveyor on the back of the machine for the filter.
A small drill bit is sent to the Z-Nano probe for inspection before drilling. If the probe senses tool wear, it automatically sends a signal to the machining center control to change the tool offset and compensate for the amount of wear.
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