The Need for Feed Units
Contributed by Frank Zagar
Edited by Jo Gardner
Because feed units are such an important part of manufacturing today, Frank Zagar contributed a comprehensive essay on the different Feed Unit Options and how to choose the right option for your shop. There will be Three installments of this article, published every Thursday.
This first installment will introduce Feed Unit selection options to consider.
A feed unit is more than just an automatic drill press. It is an automated, self-contained, modular machining unit usually offering two axis of motion-spindle rotation and linear feed. Feed Units can do everything from drilling and tapping to drill/reaming, reaming and thread rolling. The feed mechanism, which usually extends the spindle in a quill, can be driven mechanically, hydraulically, or pneumatically. A feed unit typically can perform both rapid advance and controlled feed and provides position feedback through limit sensors or encoder/resolver feedback for integration into machine control.
When a properly selected feed unit is optimally utilized, it can offer a rich payoff. Unfortunately, without an understanding of all the variables involved, it is too easy to end up with a poorly applied feed unit, a slow production rate and frustrated machinists.
Feed Unit Selection Variables:
Mechanical, hydraulic, and pneumatic feed units each have different features and functions that perform best when used for certain applications. For instance, when drilling with a carbide tool, a mechanically driven ballscrew feed unit extends tool life and enhances hole quality, because its constant feed rate translates into constant chip load on the tool. This constant chip load is crucial for the well-being of carbide tools, which are more brittle than their HSS counterparts and therefore less tolerant of uncontrolled feed-rate variation. In contrast, a pneumatic or hydraulic piston-type unit provides a constant-force feed, which may suit the requirements of a particular tool such as a deburring bit or a flow drill. A flow drill requires constant force to consistently melt the material it is cutting. The quill advances at a rate controlled by material removal. These differences are vital in your feed unit selection.
When purchasing a unit for a retrofit application, existing tools must be a consideration. A new unit purchase may or may not be tied to specific tool requirements. When buying both the tool and the feed unit, putting tool selection first can constrain your feed unit options. Today, this problem can be avoided through the flexibility offered by programmable ballscrew feed units. These units can be programmed to simulate individual requirements, including even the constant-force operation of a piston-type unit.
Next week we will cover Mechanical Feed Units: Ballscrew feed, cam feed, gear driven and leadscew. Then we will cover Pneumatic Feed Units followed by Hydraulic Feed Units.
Zagar Inc. is a manufacturer and distributor of a range of workholding solutions, multi-spindle drill and tap heads, feed units and robotic end effectors. The company’s expertise is machining both ferrous and non-ferrous materials for industries such as automotive, aerospace, electrical, medical, off-road construction equipment, hydraulic, pneumatic and high-production drilling and tapping.