Cutting Bench Time With High Speed Spindle System
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Published on 09/6/2007
Penco Tool (Ashtabula, Ohio) specializes in making very large compression and injection molds (up to 40,000 pounds) for the plastic and fiberglass industry. Owned by James Cufr and Brian Lewis, Penco serves customers primarily in the northeastern Ohio area, with some located throughout the eastern United States.
Cutting Bench Time With High Speed Spindle System
Penco Tool (Ashtabula, Ohio) specializes in making very large compression and injection molds (up to 40,000 pounds) for the plastic and fiberglass industry. Owned by James Cufr and Brian Lewis, Penco serves customers primarily in the northeastern Ohio area, with some located throughout the eastern United States. Customers for the company's large mold capabilities are concentrated in industries that include trucks, satellite television, recreational vehicles, snowmobiles, outboard motors and automotive.
Typically, large molds are rough machined on one of the large CNC milling machines, with finishing details added by EDM and bench finishing. However, this is not necessarily the ideal way to do things.
About two years ago, Mr. Cufr wanted to be able to put more detail in radial corners and save benching time. He also wanted to increase production with high speed machining. To help accomplish this, the company decided to buy a Precise high speed electric spindle system from Precise Corp. (Racine, Wisconsin) to take over some of the finishing operations. Mr. Cufr says the spindle now is used instead of EDM for some operations such as cutting grooves in a mold to create the reinforcing ribs on the back of satellite dish antennas. Also, he notes, the spindle can reduce or eliminate some bench work, speeding the finishing process and providing repeatability.
The spindle system used at Penco features a 2.7-hp (2.0 kW) Precise PKZ 25 Fixed Centerline spindle capable of speeds up to 25,000 rpm. With the spindle, Penco uses a Precise PCF 310 Solid State Frequency Converter and a Precise 7136 coolant system. CNC milling machines on which the spindle system is used include a Yoneda YD1220F and a Makino FDX2NC, as well as a Lagunmatic vertical machining center. The selfcontained system is mounted in a cabinet that can be rolled up to any one of the three CNC milling machines and is easily installed in a matter of minutes, eliminating the need to change a setup when working on the same part. Mr. Cufr reports that setup and take down can be accomplished in 15 to 20 minutes. The fixed centerline spindle design maintains the machine centerline, so CNC program adjustments are only needed to adjust the Z axis for spindle height.
Most molds are machined from P20, which is prehardened to 28 to 32
Rockwell, although occasionally some H13 material (Rockwell 40) is used.
Typically, carbide end mills are used for standard materials. For tool steel, Penco uses carbide coated with titanium nitride or titanium carbon nitride. Sizes range from about 1/16 inch to ¼ inch diameter, with 1/16 inch being common. Smaller diameters can be used, and Mr. Cufr notes that the only limitation seems to be the machine's maximum feed rate. With the smaller diameter mills, the high spindle speed provides the most effective cutting speed (sfm) to achieve optimum productivity and finish. Mr. Cufr says a typical 1/8-inch diameter carbide end mill, in a ribcutting setup, runs 11,000 rpm and feeds at 150 ipm.
Operator Brian VanLoocke says another advantage of using the spindle is that it is more efficient than the machine's main spindle for many operations and also can improve accuracy. "When you run the main spindle at very fast speeds, it heats up, so we have to adjust for the change in dimensions. It also costs a lot more to run a 35-hp spindle when the precise spindle will handle the cut."
Mr. Cufr says the high rpm finishing gives more precision and a better surface with less bench work. Typically, a 0.00211" depth of cut is used. "We're able to get the detail a lot easier and better," he explains. "In rib patterns approximately 1/8 inch wide, we can reduce machine time by two-thirds and cut bench time in half. In the long run, the biggest benefit is the quality we get."
http://www.mmsonline.com/articles/0101td1.html
Typically, large molds are rough machined on one of the large CNC milling machines, with finishing details added by EDM and bench finishing. However, this is not necessarily the ideal way to do things.
 |
| This close-up shows mounting of a Precise spindle in the machine's spindle, which does not rotate. The 2.7-hp electric spindle provides speeds up to 25,000 rpm. |
About two years ago, Mr. Cufr wanted to be able to put more detail in radial corners and save benching time. He also wanted to increase production with high speed machining. To help accomplish this, the company decided to buy a Precise high speed electric spindle system from Precise Corp. (Racine, Wisconsin) to take over some of the finishing operations. Mr. Cufr says the spindle now is used instead of EDM for some operations such as cutting grooves in a mold to create the reinforcing ribs on the back of satellite dish antennas. Also, he notes, the spindle can reduce or eliminate some bench work, speeding the finishing process and providing repeatability.
The spindle system used at Penco features a 2.7-hp (2.0 kW) Precise PKZ 25 Fixed Centerline spindle capable of speeds up to 25,000 rpm. With the spindle, Penco uses a Precise PCF 310 Solid State Frequency Converter and a Precise 7136 coolant system. CNC milling machines on which the spindle system is used include a Yoneda YD1220F and a Makino FDX2NC, as well as a Lagunmatic vertical machining center. The selfcontained system is mounted in a cabinet that can be rolled up to any one of the three CNC milling machines and is easily installed in a matter of minutes, eliminating the need to change a setup when working on the same part. Mr. Cufr reports that setup and take down can be accomplished in 15 to 20 minutes. The fixed centerline spindle design maintains the machine centerline, so CNC program adjustments are only needed to adjust the Z axis for spindle height.
Most molds are machined from P20, which is prehardened to 28 to 32
 |
| Grooves in this mold for a shower stall floor were cut with a Precise spindle. Grooves in the mold form reinforcing webs on the bottom of the floor when the part is molded. |
Typically, carbide end mills are used for standard materials. For tool steel, Penco uses carbide coated with titanium nitride or titanium carbon nitride. Sizes range from about 1/16 inch to ¼ inch diameter, with 1/16 inch being common. Smaller diameters can be used, and Mr. Cufr notes that the only limitation seems to be the machine's maximum feed rate. With the smaller diameter mills, the high spindle speed provides the most effective cutting speed (sfm) to achieve optimum productivity and finish. Mr. Cufr says a typical 1/8-inch diameter carbide end mill, in a ribcutting setup, runs 11,000 rpm and feeds at 150 ipm.
Operator Brian VanLoocke says another advantage of using the spindle is that it is more efficient than the machine's main spindle for many operations and also can improve accuracy. "When you run the main spindle at very fast speeds, it heats up, so we have to adjust for the change in dimensions. It also costs a lot more to run a 35-hp spindle when the precise spindle will handle the cut."
Mr. Cufr says the high rpm finishing gives more precision and a better surface with less bench work. Typically, a 0.00211" depth of cut is used. "We're able to get the detail a lot easier and better," he explains. "In rib patterns approximately 1/8 inch wide, we can reduce machine time by two-thirds and cut bench time in half. In the long run, the biggest benefit is the quality we get."
http://www.mmsonline.com/articles/0101td1.html