Advanced boring technology

Author: Chief Editor: Wu Tianpei
Publisher:
Publish Date: 2003-03-20
Features:
Section: Method Training requires mastering the selection of boring process plans, reasonably drafting the machining process route, and being able to determine process equipment and basic boring methods.
Selection of Boring Process Plan
I. Boring Principles
Boring methods are determined based on production types, workpiece accuracy, hole size and structure, the number of hole axis lines, and their mutual positional relationships to establish a reasonable process flow and select corresponding precision machine tools, accessories, and process equipment, aiming to produce workpieces that meet design requirements at low cost and high efficiency.
According to production types, they can be categorized as follows: single-piece, small-batch production; medium-batch production; and large-batch production.
- Single-piece and small-batch production are characterized by low quantity and high variety, with frequently changing machining objects. Universal boring machines should be selected for processing (CNC machines can be used if conditions permit). The process arrangement generally aims to concentrate operations, striving to complete multiple machining processes in a single setup. Using boring fixtures is often uneconomical, while using modular fixtures can yield good results.
- Medium-batch production features moderate quantity and variety, with periodically changing machining objects. Universal boring machines are typically used, relying on the accuracy of specialized fixtures for processing.
- Large-batch production is characterized by high quantity and low variety, with mostly fixed machining objects. Specialized boring machines (modular machines) should be used.
In some large and heavy machine manufacturing, hole processing and other boring operations (such as end faces and external rounds) can be performed by reversing the head on a horizontal boring machine or on a milling-boring machine with comprehensive processing capabilities.
II. Selection of Process Plan
Boring processing generally adopts the "face first, hole later" process flow, i.e., first roughing and finishing the main planes of the workpiece, and then using the processed planes as positioning bases for roughing and finishing the holes. The positioning bases for hole processing are typically the workpiece's installation and measurement bases. Therefore, adopting the "face first, hole later" processing sequence allows the process base to coincide with the design base, facilitating the determination of spindle coordinates based on the face when machining hole arrays, ensuring the accuracy of the boring process.
As shown in Figure 1-1a, the box workpiece has non-machined inner walls A and B, with a cylindrical pin installed at the φd hole. To prevent the pin from contacting the inner wall A, a clearance △ is provided between them (see Figure 1-1b), guaranteed by dimensions a and b.
When machining the box workpiece shown in Figure 1-1a, the A face is first selected as the roughing base to machine the C face (see Figure 1-1c), and then the φd hole is machined using the C face as the base (see Figure 1-1d). Dimensions a and b can then meet the design requirements, and the clearance △ is ensured.
If the A face is first selected as the roughing base to machine the φd hole, and then the φd hole is used as the base to machine the C face, on the one hand, the error in dimension b will affect dimension a. On the other hand, using the hole as the base for alignment cannot fully utilize machine accessories, blocks, etc., and requires a specialized mandrel with a dial indicator for alignment. This not only complicates installation and measurement but also, due to the thin wall of the box and the short length of the hole, may lead to increased errors.