Introduction

Introduction:

Design-and-Make Assignment 1 - heat-treatment effects and punch/chisel manufacturing.

In this assignment, we had to design and manufacture two engineering hand tools, a cold chisel and centre-punch.

Before that, we observed carefully the process of the heat treatment known as hardening and tempering to change the mechanical properties of the samples.

Conduct hardness tests before and after heat treatment to determine which of the materials was suitable for the tools to be made.

• For Hardness test 1, using the Hardometer instruments, we determined the Vickers Hardness for each of the three samples. Looked up the Vickers Hardness using the instrument's 30kgf diamond-point table, we recoded both the indentation value and the corresponding Vickers Hardness.
• For Heat treatment 1- hardening and tempering, we heat all of the three samples to a critical temperature before quenching rapidly in water, then re-heat again and quenching in oil to remove any brittleness and tendency to crack, chip or splinter.
• For Hardness test 2, we repeated the Hardometer tests, again and recoded the indentation values and corresponding Vickers Hardness.  

 

Heat treatment

Table result

Main body

Metal Hardening

The use of this treatment will result in an improvement of the mechanical properties, as well as an increase in the level of hardness, producing a tougher, more durable item. Tempering is a process for heat treating steel to increase the hardness and strength thereof. Quenching has two steps: heating and rapid cooling. Heating aims to get the organization of metal crystals in a phase called austenitizing. The sudden cooling seeks the martensite structure.
 In the tempering heating is above the critical temperature, which is 727ºC. The purpose is to lead the steel at a phase in which is obtained the best possible arrangement of steel crystals, for future hardness. After this phase, the steel may be subjected to further stages, depending on the needs. The temperature in this phase is austenitizing temperature. Each steel has a composition, the temperature ranges from steel to steel. Quenching is achieved at different temperatures, depending on the piece of steel composition and its goals. Therefore, the quenching of a given piece takes into account many factors.
 The workpiece itself in exposure time austenitizing temperature is taken into account when make their temper. Each has a steel austenitizing temperature, and it is one that provides maximum hardness. This temperature is obtained within furnace, which may be flame or by electrical induction. Depending on customer requirements, austenitizing, and therefore tempering, will occur only in the part surface or across it.
 The second stage of cooling is quenching, which must be sharp in water. The rapidity of cooling is important to prevent the steel change to different phase from that obtained in the austenitizing temperature (more martensitic structure). Often, after hardening, the part is subjected to tempering.
After that, heating again and cooling in oil.

cold chisel engineering drawing

                 

centre punch engineering drawing

Manufactured items