February 2014 Archives

The 3^rd of the representative element technologies, Insertion Assembly technology is explained. The automated assembly operations (Low cost automation) are composed of multiple automated elemental operations that are simple. In our technical tutorial course, "swaging", "screw fastening", and "insertion assembly" technologies are explained as the representative element technologies.

(1) About Insertion Assembly Technology

・Insertion assembly is a procedure to process the following operations manually, or by the use of fixtures/devices.

・Interference fits such as press fitting realize functionalities such as (1) fixing, (2) positioning, (3) orientation fixing, (4) force transmission.

・Clearance fit insertions are for, (1) positioning, (2) guiding, (3) joining pre-process, (4) joining.

(2) Characteristics of insertion assembly technology

1. Advantages

・Since the insertion assembly is performed in one direction, it is suitable for automating.
・Highly accurate assembly automation is possible based on accuracies of the components.
・Post assembly re-working and disassembly are possible.

2. Shortcomings

・Configuration designs and quality (accuracy, surface conditions, etc.) of the mating components largely affect the insertion assembly.
・It is very difficult to automate insertion assembly processes that require highly skilled manual operations.
・It is difficult to disassemble defective workpieces that are insertion assembled by automated operations.

The screw fastening unit is the most important of the automated screw fastening mechanism.
Representative screw fastening methods and fundamental structure examples of the automated equipment is explained below.

(1) Screw fastening methods

Below is a representative mechanism of a screw fastening section.

There are following fastening methods of screw fastening units. Variations in the fastening force are improved as a)>b)>c)[High accuracy].

	a) Torque control method	: Method of transmitting the power of electric motors, etc. to the screw fastening unit's rotating shaft as rotary torque.
	b) Angle control method	: Method of controlling fastening angle by a motor with encoder.
	c) Yield point method	: Method of controlling the fastening force by detecting the deformation behavior of fastened screw.

(2) Example of screw fastening unit

[Fig.1] is an example of an automated nut fastening device with 6 axes of fastening actuators (nut liners) mounted in parallel. Nuts are fastened after the 6 axis nut fastening actuator mounted on a linear guide is positioned by an air cylinder.

Screw fastening failures are classified, and the fastening device trouble countermeasures are explained below.

(1) Screw fastening failures and factors classified

Screw fastening failures can be classified as the following.

Below are the defect contents related to the screw fastening devices.

a) Screw fastening process failure

	・	Automated fastening unit control failure
	・	Screw fastening errors (Misalignment, diagonal fastening, etc.)
	・	Screw positioning error

b) Screw faster tool flaws

	・	Worn or missing screw driver bits
	・	Worn screw chuck
	・	Inadequate maintenance on fastener tools

(2) Examples of screw fastening device troubles and countermeasures

1) Screw fastening device (case of pneumatic screw driver) trouble countermeasure examples

	a)	Due to the reaction forces generated during the driving operations, air driver operations tend to fail after some usage intervals.
	b）	Many cases are caused by wear, foreign substance adhesion, rusting and seizures of the rotating shafts. Lubricant is applied and For/Rev rotations are to be repeated.
	c）	Check on air supply pressure.

2) Screw fastener tool flaw trouble countermeasure examples

	a）	Maintain spare parts and periodically (qty. managed) replace screw driver bits assuming that the tips deform by wear.
	b）	Screw chuck parts are the same as a).

3) Periphery management of screw fastening device for safe operations

In order to maintain high operational rate stably, not only the proper management of the automated devices but assembled parts/products quality management maintenance affects prevention of operational failures.

[Examples of managed items]