HMC or HBM?
January 1, 2010
Traditionally, work done on a large horizontal machining center (HMC) could not be confused with work done on a horizontal boring mill (HBM). However, as technology in both camps evolves, the line between these two systems gets blurred.
If you are producing parts in high volumes, then the pallet system associated with your HMC means that you have made the correct choice. However, pallet changers now can be added to a boring mill. Also, if a part requires multiple setups to be completed, then it is likely best-suited for an HMC.
“Typically, HBMs have been for heavier workpieces with small batch sizes of five to seven pieces,” said James Bonnell, national sales manager for Toshiba Machine Machinery Co. “Setup involving manual operation of the pendant is usually characteristic of HBM work. HMCs are less rigid and have smaller headstock and machine castings.”
Using a quick-change subplate system on an HBM provides flexibility and rigidity covering the best of both worlds, however.
“The tendency to move to the HBM format also has to do with smaller batch sizes and the fact that the W axis on an HBM can allow for small and large parts to be machined with ease of setup,” said Bonnell.
In addition, boring mills usually can handle heavier table loads and have larger-diameter table couplings than HMCs, which is particularly important when machining off of the table’s centerline. Also, HBMs can cost up to 35 percent less than an HMC with the same size work envelope, but generally do not come with a pallet changer, according to Bonnell.
“HMCs in the past have been faster, but now HBMs are available with air lift systems in the X, Z, and B axes for higher speeds,” said Bonnell. “Also, a hydraulic and cable pulley system in the Y axis of HBMs can now offer higher speed in that axis for smoothness of operation, which is typical of an HMC. “
The integration of software and hardware in both HMCs and HBMs is bringing these machines closer in terms of machining repeatability and accuracy. According to Bonnell, with Toshiba’s CNC Shape function, large HBMs can be fined-tuned to function like a very large HMC.
The Technology
New technology has meant an increase in the types of work that can be done on these machines. Some of this technology includes:
- A high-speed W axis for finishing operations.
- Random angle clamping on the table as opposed to the typical 90-degree shot pin approach.
- Air lift systems for heavy workpieces.
- Manual independent pendant for ease of setup.
- Mist lubrication to spindle bearings as opposed to an oil cooling jacket.
- Machines with cast components as opposed to fabrications.
- Machines that are prepared for PHSR (Pre-Start Health and Safety Review).
“Typically, HMCs have higher acceleration/deceleration rates and rapid traverse rates, reducing cycle times for quicker throughput,” explained James Spannbauer, global product leader for MAG Industrial Automation Systems.
MAG’s HMCs can be purchased with a fixed or live spindle, thanks to new technology. Also, a full enclosure on the machine allows high-pressure coolant to be used in chip removal.
Live spindles and higher spindle torque, features not always available a few years back, result in machines that can do more than their name implies.
“Many customers perceive an HMC as a drill and tapping machine and an HBM as a heavy boring and milling machine,” said Spannbauer. “I believe this gap is closing [to] where both machine types can share the same workpieces.”
With the addition of a live spindle on an HMC, users have the ability to reduce tool length and increase stiffness for long reaches on parts.
Higher-speed and more powerful spindles with faster chip removal are mandatory when machining materials such as aluminum. New HMCs can handle the high chip removal rate not typical on HBMs.
“Customers are also machining harder materials such as titanium or stainless steel [on HMCs], requiring higher torque spindle and stiffer machine designs,” said Spannbauer.
Boring machines have this stiffer configuration and have a much higher metal removal rate, but at lower RPMs. They also offer greater flexibility thanks to special attachments and more head configurations than HMCs.
“Regardless of the machine configuration, HMC or HBM, most customers are looking for configurability and quick deliveries,” said Spannbauer. “Choice of headstock is becoming important and, finally, coolant systems are becoming increasingly important on both the HMC and HBM products to increase productivity.”
For more information, visit www.toshiba.ca and www.mag-ias.com.
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