Designing a gearbox of a milling machine

Contents

Table of contents

Source Data

Features of design and milling machines of the nonconsonic type

Prototypes of machine tools

Comparison of technical characteristics of the machine in question

Specifications of the selected machine

Design Tasks

Calculation of limit cutting modes for engine selection

Kinematic calculation of the main motion drive

Determining the Numbers of Gear Teeth

Determination of actual frequencies

Kinematic diagram

Power calculation

Design calculation

Calculation of pre-spindle shaft

Refined calculation of pre-spindle shaft

Calculation of shaft 3 for strength

Calculation of key connections

Calculation of 3 shafts for static strength

Bearing Strength Check

Pre-spindle shaft strength calculation

Speed switching system

Selection and description of lubrication system

General description

Nonconsole milling machines (BFS) are designed for the treatment of flat and shaped surfaces of body parts of medium and large sizes in a variety of conditions of the main production of machine-building enterprises.

The load-bearing machine system consists of rigid parts, a developed spindle group and the main drives of high power, providing the possibility of working in optimal cutting modes with any tools, including ultra-hard materials and ceramics.

Sliding friction pairs (hardened steel or cast iron - plastic pads on movable units) on the main bearing faces and rolling on the side orienting sides are used in guide movable units.

Main motion is driven by asynchronous electric motor through stepped speed gearbox or by adjustable electric motor through two-, three-stepped overpass. Powerful spindle units have hydraulic unloading mechanism.

Feed drives use adjustable motors in combination with ball screw gears.

Classification of Milling Machines

Milling machines are divided by purpose into the following machines:

- general purpose.

- specialized.

General purpose milling machines:

1. - cantilever-milling.

A) horizontal-milling.

B) vertical-milling.

C) universal horizontal-milling.

D) wide-universal.

2. - boneless-milling.

3. - longitudinal-milling.

4. - carousel-milling.

Milling machines specialized:

1. - schlycefreser.

2. - threaded rubber.

3. - toothfreser.

4. - copying and milling.

4. - milling and cutting.

Main characteristics of milling machines

- the number of speeds - 18... 24.

- speed range - 50... 2000 rpm.

- denominator of rotation speed series ȹ - 1.41.

- deviation of the form - 20... 40 μm.

- surface roughness Ra 2.5

Peculiarities of assembly of unconsonless milling machines

The name "bed-type milling machines" or unconsonless machines comes from the type of frame on which the entire machine is assembled. An integral feature of this structure is the constant position along the height of the machine table and, therefore, the workpiece. Unlike bed-type milling machines in cantilever cutters, the height position of the table can be changed. A feature of the appearance of milling machines with a bed bed is their outer contour close to an isosceles triangle, having a wide base and providing optimal structural stability

The design of the bed table milling machines ensures accessibility to all machine units and ease of maintenance. The wide support surface of the table allows the installation of large mass blanks. According to the location of the working spindle, milling punks with horizontal and vertical spindles are distinguished. Most bed-type milling machines can be equipped with interchangeable milling units of one kind or another, it is possible to create combined structures.

Milling tool is moved relative to workpiece along three mutually perpendicular coordinate axes. If the tool moves along the axes, the DIN 66217 the corresponding translation directions are indicated by X, Y, and Z. The Z axis is taken in the direction of the tool rotation axis. If you go in a conditional way, for example, from the workpiece, and then from the tool to the foundation of the machine, then the movement along the coordinate directions of the movable units is carried out in a sequence characteristic of one or another structure. The bed and the bed of the machine are rigidly connected to each other .

Moving the workpiece along one and the tool along two axes: this family distinguishes the fact that the table lies directly on the bed, which creates special advantages for servicing the machine, loading and removing the workpieces. In addition, the effect of the mass of the workpiece on the information of the entire machine is very small, especially when changing the position of the workpiece if the feeding movement is carried out by the workpiece. This family can be called "table milling machines ."

Vertical Milling Machine Process Operations

Milling machines are designed for cutting using a rotating tool with one or more cutting edges. Depending on conditions of interaction of cutting edges with workpiece periodically varying in value and direction of cutting forces occur. As a result, high static and dynamic loads occur during machining on milling machines.

Speaking about the classic models of vertical milling machines, without additional functions, non-standard components, they are designed to perform such technological operations:

bore;

milling;

processing of endcaps;

sampling of slots;

cutting the metal layer;

drilling.

The accuracy of the task on such equipment is quite high. In the design of a vertical milling machine, the spindle head acts as a speed box, which can be regarded as an additional feature. The head moves vertically along the rack guides. The spindle with the sleeve can also be moved axially.

Main drive

The main drive implements a large range of spindle speeds at constant transmit power. In the main motion drive, DC motors with stepless regulation and AC motors with a gear box controlled manually or hydraulically are equally used.

Features

The nonconsolvent machine differs from the cantilever machine in that its crusade table is mounted on a stationary bed. Its surface makes movements exclusively in transverse or longitudinal direction. A cantilever vertical unit is often unable to mill heavy and large products, but non-cantilever installations cope with them without problems. In addition, the feeds of machines without a console are made by engines in which the number of revolutions (gears) is continuously selected.

The vertical milling machine, due to its sufficient rigidity and high power of the drives installed on it, makes it possible to work with a hard alloy type tool. Machines of the vertical type, as a rule, are distinguished by a high drive power, which, in combination with a hard alloy tool, creates a very productive tandem.

The weakest link in the power circuit of the AIDS system (machine, accessory, tool, part) determines the permissible cutting modes that can be adopted during processing of the workpiece. Milling of inclined, flat, convex and concave complex surfaces, as well as high accuracy of repetition during positioning require high geometric accuracy of the machine and non-locking design of feed guides and drives. In order to achieve optimal roughness of machined surfaces, the tool spindle must be installed in supports without clearances in radial and axial directions, without beating in these directions.

In order to prevent and absorb torsional oscillations in order to ensure higher tool stability, the tool spindle shall be driven with maximum uniformity in both rotation directions and reversing. This object is satisfied by a worm drive or a cylindrical gear train with a permissible small gap between the teeth and a large moment of inertia. Some special requirements for the table feed drive and caliper drive are established for associated milling.

These requirements are best met by the following designs: a rack drive with two gears turned relative to each other (to take out a radial gap in engagement), drive gears, that is, a split gear wheel with preliminary tension; worm rack gear with preliminary tension or hydrostatic overpressure between worm turns and rack teeth, as well as a ball screw pair with a double prestressed nut.

Milling Machine Movements

The most common embodiments of the three main types of machines are characterized by the difference in the position of the spindle relative to the machine table and in the communication of the three mounting movements to the workpiece by means of slides mounted on the cantilever. In addition, there are versions of machines in which only vertical and longitudinal in some cases rotary) movements are realized using the console. Lateral displacement is performed by movable spindle unit sliding along guides on bed.

Docking and basing tools.

To fix the tool, ISO attachment structures are used in combination with an electric or hydromechanical clamp drive.

Expansion of capabilities is achieved by using special devices:

- horn shackle and intermediate support for milling.

- vertical milling head.

- rotary milling head.

- universal rotary milling head.

Fixation of workpieces and their basing.

The machine table is used as the installation base. The following is attached to the blank table:

- using keys or slats.

- struts with screw grips.

- special devices (USP, etc.).

- round turning tables.

- rotary dividing tables.

-NC round tables.

- dividing heads.

Control the processing process.

Increasingly, machine tools with manual control and central drive are being replaced by machines with separate drives and automated control. According to the level of automation, the following types of control can be distinguished:

- manual control with indication of actual table position.

- software cycle control.

- software numerical control directly from the machine console.

- copying control systems.