Setting up an assembly line to manufacture UPS systems & inverters

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With the demand for power backup devices like inverters and UPS systems increasing at a fast pace, many players, including a large number of SMEs, are venturing into manufacturing these devices, while those already established in the sector, are planning to expand their existing facilities. This article gives you an overview of the assembly process needed for inverters and UPS systems; the different types of machines, equipment and tools required; how one can acquire these tools and equipment; and the investments involved in setting up an assembly line.

By Srabani Sen

Tuesday, July 12, 2011: The step by step process
The assembly of UPS systems is divided into a number of processes, erformed by operators at different stations on the assembly line or the conveyor. Specific operating procedures (SOPs) are written down for every station, in which all activities to be performed are mentioned along with their tools, instruments and zig (a common inverter that is used to test all PCBs). The list of SOPs is pasted on the instruction board placed at the assembly line. Operators working at a particular station perform operations as per the SOP assigned, as the product moves from one station to the next on the conveyor. After an operation has been completed and the product inspected, it is passed to the next station for further work, and the process goes on in a similar way till the last station.

First of all, cabinet base grommets, lead bases, AC fuse holders and output AC sockets are fitted in the cabinet. This process is called cabinet preparation. Then the wiring and soldering of the back plate components are done at the back plate wiring stage. At the  transformer fitting stage, the main transformer is fitted. Then the battery wire is inserted and fitted on to a tested and okayed PCB. After this stage, the drain wires of the transformer are fitted to the PCB, which is then fitted on to the cabinet with screws. Then connectors are inserted according to the block diagram of the product, and the front fascia is fitted.
At the next station, electric and internal physical parameter testing is performed by the line testing engineer, who checks all the parameter values of the product against the specifications mentioned in the SOP of that station. At the top cover fitting station, the top cover is fitted with the help of screws. To ensure the reliability of the product, all the electrical and physical parameters are verified once again at the final testing station. If any product does not pass the test, then it is sent back for re-work.

After the final tested station, there comes packing station, where serial number stickers, for the purpose of traceability, are pasted and the final packing of the product is done.

Then comes the outgoing quality control (OQC) station, where some samples of the products are randomly checked for reliability. The OQC engineer checks the complete packed samples thoroughly—physically, aesthetically and electrically. Until the lot is accepted by the OQC in-charge, based on the parameter requirements, the whole lot cannot be moved to the finished goods store (FG store). To ensure the reliability of the product manufactured, some samples are again checked at the endurance lab. When this lot is accepted by the electronic lab testing (ELT) engineer, only then it is dispatched.

Other vital requirements

Internal quality control (IQC) labs with equipment to thoroughly test incoming raw material is a major requirement. A dust free, neat and clean environment is a must, for which an air handling unit is required.
Engineers and other professionals in plants ensure the quality of products at the following stages:

  • Quality of incoming raw material
  • Checking the quality of products at the pre-despatch stage
  • Supplier quality assurance and capability analysis
  • Internal quality audits as per ISO 9001, ISO 1400, CE and UL requirements

To ensure complete quality control, all raw materials are checked strictly as per established quality standards and requirements, which are listed in the inspection reports. Individual supplier assessment and supplier rating is done depending upon the rejection levels at the incoming quality control stage. If any rejection occurs at this stage, a first information report along with a CA/PA report should be sent to the respective supplier, purchase department and stores. Some precautionary steps should be taken before the consignment is despatched to clients. In a nutshell, 4Ms—man, machine, method and materials, should be looked into to run the process smoothly. All the machines, tools and equipment required for high quality product, should be acquired.

You can acquire the machines, tools and equipment from local suppliers/traders. Many companies self design the machines and equipment as per their requirements.

Research work needed

Before importing, purchasing from domestic suppliers, or self designing the automatic conveyers, automatic testing rigs, or other tools and equipment, a thorough process study should be done. Manufacturers should first do aggressive market research and find out about the key players. For standard tools, their suitability must be evaluated against actual  individual requirements, durability, efficiency and the cost of all other similar products available in the market before deciding on the optimum solution. You can acquire quotations and technical specifications from different suppliers of different brands, compare them with one another and select the best deal.
If you are designing your own assembly line, you may face certain challenges. The role of every machine and piece of equipment needs to be visualised on paper in accordance with the process flow. That may take a lot of time and effort. But once you are ready with your final blueprint containing each minor detail, then getting the assembly line manufactured as per requirements will not be difficult.
When choosing any machine, tool or equipment, consider the skills required to use the machine, the capacity it can handle, its usage in the industry and the service lead time promised by the machine maker. Also, find out about the availability of refurbished machines, spares in local markets and the lead time for importing.

Maintenance

All automatic testing rigs are very sophisticated, so they need periodic cleaning and checking. Conveyer lines and pneumatic tools also require periodic cleaning and oiling. Preventive maintenance is important as far as imported machines are concerned. An inhouse technically sound maintenance team can take care of the preventive maintenance.  So periodic calibration, proper oiling on a daily basis, and sometimes external preventive maintenance are advisable. (Please refer to the table for details.)

Some check points

The complete assembly line should be planned on paper first with fine detailing of the process, the capacity to be built up, and proper assembly line setup design according to the planned capacity. Keep in mind the easiest movement of materials in a single line flow, and future expansion plans. Also, leave room to plan for the connection of other tools and instruments, as and when required.
You should also decide about the capacity you want to target and the level of reliability you want. Check your budget as well. Calculate the approximate cost of the whole setup.
Make the project timeline sheet and keep studying the timeline track record of all connected activities so that they are all completed in coordination with one another. Once the setup is installed, always try to utilise it optimally. Maintain all tools, machines and instruments properly. To check the effect of static charge (which is harmful to electronic devices), an antistatic environment at the stations is essential.
Certification/licence
No specific certificate or licence is required to start an assembly line. You only need to get all statuary approvals from local government departments as per industry laws, like NOCs from the local and Central government planning departments and pollutioncontrol boards, apart from registering the firm with the relevant industrial departments, and ensuring that a copy of the registration and the factory licence is with the concerned departments. Further, you can apply for quality certifications (ISO 9001:2008), work towards globally approved environmental policies (ISO 14001:2004), CE compliance, RoHS, etc.

Costs involved
The cost of setting up a UPS and inverter assembly line depends on the size of the plant  and the capacity you are planning. For example, for a capacity of 400 units (eight working hours), the cost incurred is around Rs 1.5-2.5 million (Rs 15 -25 lakh) (including a DG set). Naturally, this figure also depends on the quality and design of the assembly line and the other facilities incorporated into the working environment.
The investment on machines, tools and equipment accounts for about 80 per cent of the total cost (including the cost of the conveyor) of the assembly line setup. Around 2-3 per cent of the total cost goes towards annual maintenance, depending on the type of the assembly line.

You can go in for finance schemes offered by different banks. You can also take the machines, tools and equipment on lease or rent.

Tools, instruments and machines used in UPS/inverter assembly line

Instruments

Function

Maintenance requirements

Maintenance source

Digital CRO

To check output waveform and parameter values

Periodic calibration

External lab

High voltage tester

Electric leakage, HV breakdown and shorting

Periodic calibration

Buyer

Torque wrench

To check the torque of electric and pneumatic screws/nut drivers

Periodic calibration

External lab

Weighing scale

To check the weight of the UPS/inverter

Periodic calibration

Buyer, to check against an externally calibrated scale

Humidity and temperature meter

To know the temperature and humidity

Periodic calibration

Buyer, to check against an externally calibrated scale

Test panel zig

To check all the electric parameters of the inverter/UPS

Periodic calibration

Buyer, to check against externally calibrated multimeters and clamp meters

Tubelight, bulb load & CFL load test setup

To check working and electric parameters on inductive and capacitive load along with bulb load

To check whether they are in working condition or not (switches and load)

Buyer

Hydro meter

To check the specific gravity of the battery

Periodic calibration

Buyer, to check against externally calibrated meters

DC power supply

To check PCBs on it, apart from other components

Periodic calibration

Buyer, to check against externally calibrated meters

Multimeter

To know electric parameters like voltage, current, etc, and also to test the diode, resistance, capacitance, etc

Periodic calibration

Buyer, to check against externally calibrated multimeters and clamp meters

Clamp meter

To check AC and DC current

Periodic calibration

Buyer, check against externally calibrated multimeters and clamp meters

Plastic hammer

For top cover and cabinet setting

NA

NA

Pneumatic screw/nut driver machine

To tighten nuts, bolts and screws

Proper oiling on daily basis, periodic calibration of its torque, to check for air leakage and for preventive maintenance

Buyer or seller

Variac

To vary AC voltage for measuring high cut and low cut

Periodic calibration

Buyer, against externally calibrated multimeters and clamp meters

Stripping machine

For stripping of the final production

Periodic check of its heater and motor. Also to have external preventive maintenance

Buyer as well as seller

Automatic double sided tapping machine

For putting tape over flaps of UPS box

Periodic preventive maintenance

Seller/external

Air compressor

To operate pneumatic screw and nut drivers

Periodic calibration for its pressure meter, and auto cut working. Releases its pressure at the time of ending work so that air does not condense inside GI pipes and the tank itself. This will prevent tools from malfunctioning when water goes into mechanical moving parts.

Buyer, against external calibration meters

DG set 125 kVA

For standby electricity generation

AMC/preventive maintenance, and testing of different load values against its capacity, for optimum efficiency, earth resistance check

Buyer and AMC (seller/external)

Hot air gun

For shrinking heat shrinkable sleeves

To check for proper functioning

Buyer

Screw driver

For tightening screws

To check its teeth

Buyer

Nose plier

For tightening nuts/bolts

To check its jaws and nose

Buyer

Glue gun

For melting glue sticks

To check its functioning

Buyer

Soldering station

For soldering delicate/critical components

Periodic calibration

Buyers, against calibrated temperature instruments

Soldering iron

For soldering components

To check its TIP and the temperature on its TIP

Buyer

Fire extinguisher

For safety precautions in case of fire

Periodic refilling and to check how it works

Seller/external

Hydraulic pallet truck

For moving material

Periodic oiling of moving parts and periodic preventive maintenance

Buyer and seller (preventive maintenance)

Assembly conveyor

For moving products from one station to other; to work on the product; to hold raw material, to hang the SOP, and for line-balancing

Periodic oiling of moving parts and periodic preventive maintenance

Buyer and seller (preventive maintenance)

JUMPRR (JV )

Inserts jumper on PCB

Preventive maintenance

 

Axial

Inserts axial components on PCB

Preventive maintenance

 

MK-1C (SMT)

Inserts chip components on PCB

Preventive maintenance

 

Radial (RH-6 )

Inserts radial components on PCB

Preventive maintenance

 

Oven

Double solder bath facility for SMD components

Preventive maintenance

 

Automatic optical measurement machine

Detects missing, reverse, wrong values and shorting

Preventive maintenance

 

Incircuit testing machine

Complete PCB component checking including missing/wrong value/reverse /lifting/shorting

Preventive maintenance

 

Bar code scanner

Scanning of finished goods

Preventive maintenance

 

Source: Truepower International and Su-Kam

Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine

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