Beginners Guide to uPVC Manufacturing Process

Basic Introduction to uPVC Manufacturing process

Upvc Window Manufacturing Processes

Material

Upvc extrusion : Length normally 6.0m or 6.5m

Window configuration

Externally glazed (Meaning all the glass is beaded from the outside of the house). This style is not as common within the UK as it is less secure. It can however be more aesthetically pleasing as there is no reverse butt welding required. This style can also be supplied with an end milled or “V” welded transom and mullion joint.

Extrusion types

“L” shape : Outerframe profile.

“Z” shape : Sash profile

“T” shape : Transom/Mullion profile

Internally glazed (Meaning all the glass is beaded from the inside of the house). This style is the most common within the UK as it is more secure however it requires an additional process to be done on the outerframe. This process is called “Reverse butt” which consists of the outerframe being cut at 90 degrees at the point were the transom will be welded. The outerframe will then be welded together again with one piece reversed at 180 degrees to the other. The purpose of doing this process is so the sash can still be opened outwardly when assembled.

Extrusion types : “L” shape : Outerframe profile

“T” shape : Sash profile

“Z” shape : Transom/Mullion profile

Sawing and Machining

Cuts

a) 45 degree mitre cut in preparation for corner welding of sash and outerframe

b) 90 degree (straight cut) in preparation for reverse butt welding of outerframe

c) Arrowhead cut in preparation for Transom and Mullion welding into the outerframe

d) **Bevel cut (Combination of 45 & 90 degree angles) in preparation for reverse butt welding of outerframe

** (This process is normally done on a CNC Sawing & Machining Centre).

Machines : Single and Double Head Mitre Saws (Example : Make &Model : Elumatec MGS72, DG79, DG142, Emmegi 40S, Norma-400, Classic Star 500, Stuga Autocut.

Other popular makes : Haffner, Wegoma, Kombimatec, STB, Mecal, FOM, Pertici, Avantek.

“V” Notching

This is when a “V” is cut into the inner face of the outerframe in preparation for welding the “arrowhead” joint. The arrowhead is cut using the “Z” or “T” transom profiles depending whether the window is internally glazed or externally glazed.

Machines : “V” Notch Saw : Example : Make & Model : Pertici VC721, Elumatec KS101.

Other popular makes ; Haffner, Wegoma, Kombimatec, Avantek.

3) Machining (Routing) :

The machining process is were you prepare the window to accept the hardware (Handles, locks, gearing) and for ventilation. It is also to prepare the drainage and equalisation slots to allow outside water to pass freely thorough the internal chambers of the profile so as not to enter the inside of the house.

Machines : Copy Router, Drainage (Waterslot) Router, Vent Router. : Example : Make & Model : Pertici FC106, ML142, Elumatec GF171, WSF, MLA A21, WS32. Stuga Ecoline

Other popular makes : Haffner, Wegoma, Kombimatec, Avantek

Special note : All the above processes from Main sawing - “V” Notching - Machining can be done using a CNC Sawing and Machining Centre. : Stuga Autoflow, ZX5/E, ZX5/S.

Steel Reinforcement

In most cases fabricated thin gauge steel bars will be used to reinforce the window to give it the strength and rigidity. The steel is cut to the required length which would normally be approximately 10mm to 20mm less than the cut length of the Upvc profile and then inserted into the reinforcement chamber which is located in the centre of the Upvc extrusion. The steel is then held in place by fixing screws. Windows can also use “regrind” reinforcement which is basically manufactured using old replacement windows or rejected extrusions which are broken down and then extruded to form a solid bar which can then be inserted and fixed inside the reinforcement chamber. The benefits of regrind reinforcement is that it can be inserted into the main profiles before cutting and then welded as normal during the welding cycle. This enhances the corner strength as well as the overall thermal efficiencies of the window. The down side is that regrind is not as strong as steel therefore it cannot be used for all applications and styles. Especially Upvc doors which require to have steel inserted due to the higher risk of expansion and contraction.

Machines : Coldsaw, Bandsaw. : Example : Make & Model : MACC 250DV, MACC Special 280M.

Welding

Main Welding

The most important part of the process in manufacturing Upvc windows is the welding. It is important that the welding machine is kept in good condition and regularly serviced to maintain accuracy and to keep consistency across all the welded joints. This will prevent poor welds which is the most common cause of joint breakages and inaccuracies when performing the cleaning operation post welding. It is also vitally important to instil good housekeeping of the welding fixtures as bruised or damaged fixtures are also common causes of poor welds.

The most widely used welding machines amongst window fabricators, whether small, medium or large, is the In-Line Combination Welder. They can either be supplied in three, four or five head versions and can have additional functions were the heads can swivel internally to allow

for the welding of “H” joints. All UK windows styles, whether complex or not can normally be welded on this type of machine which is why they can be found in every Upvc window fabricator. The larger producers will also have one or several of these types of welders in their workplace as they still have a vital role to play even when there is more automated welding machines in place. The In-line welders are then used offline to produce the non standard window styles which take longer to produce or they are used as “build up” welding machines to produce all the welded joints like a “H” weld or a crucifix joint in preparation for finishing on the automated four, six or eight head welding machines.

Reverse Butt Welding

To understand the reverse butt welding process, please refer to the first page under “Internally glazed”. This process is performed prior to completing the welding of all other peripheral welds on the corner and transom joints. The most common machine used in the industry is a single head welder. The heater plate is flat and the back fences are normally variable angle that can be adjusted between 30 deg. to 180 deg. When welding a reverse butt joint the back fences must be set at an angle of 180 deg. The “burn off” will normally be between 5mm to 6mm and the “weld seam limitation” will range between 0.2mm to 2.0mm depending on the type of welder and also the customers preference. An important point to note is that when a reverse butt weld is performed the burn off can be up to 1.2mm less than what the welder has been originally specified to do at 90 deg. For example, if the welder has been specified during its build to weld a 90 deg. angle at a burn off of 6mm then it will only burn off 4.8mm when doing a reverse butt weld. It is therefore important to specify the exact burn off required at 180 deg. when ordering a machine.

(I will refer to the different terminology used within the manufacturing processes at the end)

Crucifix (Cruciform) Welding

Crucifix welding or cruciform welding is when you weld three or in some cases four pieces of profile together to create a cross. This can be seen in some complex window styles like a four or six pane window. The crucifix joint can be performed on a dedicated single head Crucifix welder which has an “X” shaped heater plate which allows for four separate lengths of profile with “arrowhead” cuts to be welded simultaneously. The other method of producing a crucifix joint is to cut a “V” notch into one side of a profile then weld a mating arrowhead into this to form a “T” joint. The opposite “V” notch would then be cut out in preparation for the second arrowhead to be welded. This process takes longer and involves having a “V” Notch saw and an In-line or single head welding machine which has a “V” shaped heater plate. These heater plates are the most common used in manufacturing windows and are found on every multi head In-line welding machine. The process of forming a Crucifix joint is exactly the same as a reverse butt joint were you have to manufacture it prior to completing the welding of all other peripheral joints.

Corner Cleaning

The corner cleaning process is performed post welding and its sole function is to clean all the excess weld or (sprue) around the complete welded joint. The transom and crucifix joints can also be cleaned using a combination corner/transom cleaner. The main points of any corner cleaner is what is the maximum height it can clamp and what is the minimum internal dimension it can clamp. This is important as profiles evolve they are becoming taller and also the internal clamping needs to be correct to suit the customers minimum “transom drop”.

The most common corner/transom cleaners in the UK market are manufactured by URBAN and to a lesser extend, ROTOX. Both of which are manufactured in Germany. The most common single head corner cleaner amongst the small, medium and large fabricators is the Urban SV530 and to a lesser extent the Rotox EPA379. It is common for the larger fabricators who have two or four head automatic corner cleaners to also have one or several single head corner cleaners which they would use offline as “build up” machines for cleaning complex window styles.

Beading

The Beading of a window is the final process before assembly. The most common angle of cut at each corner joint is 45 degree as this is the quickest and easiest to produce. The level of quality and consistency can however be difficult to maintain as the cut of the angle and the measurement of the cut length must be accurate otherwise you will see gaps in the joint. With new technology in beading machinery the margin of error is drastically reduced due to advances in bead holding fixtures and electronic measuring wands which give far greater accuracy. The other method of beading is to “overscribe”. This is a longer process to manufacture as it involves using a bead saw or chop saw which will be used to cut two beads at 90 degrees and a bead end milling machine to mill out the end of the two remaining beads to the shape of the external face of the bead. This method is normally used with fabricators who do not have a good quality beadsaw or they just prefer this particular finish. It can also be the preferred choice if they are working with less flexible bead profile as its easier to remove from the window if sealed units need to be changed. en none 0

Draft