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IndustryArena Forum > GENERAL MANUFACTURING PROCESSES > MILLING > Uneven surface finish on steel
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  1. #1
    Join Date
    Apr 2020

    Uneven surface finish on steel


    I was facing a part. But, the surface finish of the part is uneven, only one small part has mirror-like finish and feels 'flat', the other has tool marks. Can anyone explain what could've possibly gone wrong? I'm pretty sure that the part is clamped down hard enough. Hasn't check runout and the inserts have different heights, I used the lowest insert to setup for my z-axis.

    material: mild steel
    tool: 50mm shell mill with 4 AMPT1604 inserts at 90 degree
    speed: 382rpm
    feed: 76mm/min
    DOC: 0.15mm
    stepover: 75% of tool diameter
    coolant: blast


  2. #2
    Join Date
    Jun 2010

    Re: Uneven surface finish on steel


  3. #3

    Re: Uneven surface finish on steel

    The surface defects of different steel plates have different appearances: serial number | defect name | possible process of generating defects | possible causes
    Surface defects of cold-rolled steel plate and steel strip
    1. Surface defects
    (1) Defects that are not allowed to exist in steel plates and steel belts
    1Bubble | Steelmaking | Bubbles are produced during steelmaking, but are not welded during hot rolling, pickling e68a84e799bee5baa6e997aee7ad9431333332623262 exposed after cold rolling
    2 Cracks | Steelmaking, hot rolling and cold rolling and various cnc machining procedures | due to thermal stress in steelmaking, rolling deformation or stress concentration caused by processing
    3 Scars or nodules | Pickling and cold rolling | Pickling does not wash out the oxide scale, which is embedded on the surface during rolling to form scars
    4Cracking | Cold rolling, galvanizing and smoothing | Caused by excessive tension, excessive tension fluctuation and unstable tension
    5 Inclusions | Steelmaking | Reasons for Steelmaking
    6 Folding | Hot rolling, cold rolling | Metal that is viscous during rolling is rolled again and mounted on the surface of the plate
    7 Delamination | Steelmaking, hot rolling and cold rolling | Composition segregation and microstructure segregation, large inclusions, etc. during steelmaking are caused by delamination during the rolling process
    8 Black film or black belt | Pickling | Caused by poor drying after pickling
    9 Emulsion spots | Cold rolling and smoothing | Caused by the emulsion remaining on the surface of the machining steel strip
    10 Corrugation and folding | Pickling | Pickling, etc. (to be checked)
    11 Barbs or burrs | Shearing process | The cutting blade is not sharp, the upper and lower cutting blades are staggered at a large angle, and the cutting blade angle is not accurate
    (2) Defects that are allowed to exist and are divided into different surface quality levels according to their degree
    1 pits | cold rolling, smoothing and smoothing | due to the adhesion of the plastic matrix metal to the surface of the roller rotating at high speed during rolling
    2 Scratches | Each process and the lifting process, etc.
    3 Scratches | handling, lifting process
    4 Blue oxidation color | Cold rolling and smoothing | Due to rolling friction, the base metal is heated to cause the base to bluish, especially the strip edge is more likely to form this defect
    5 Light yellow pickling color | Pickling | Caused by not drying after pickling
    6 Roll indentation | Cold rolling, smoothing and smoothing | Rolling reasons
    7 Scratch | handling, lifting process
    8 Dimples | Cold rolling | Rolling reasons and surface inclusions are rolled out of the substrate surface to form pits
    (3) Other surface quality defects
    1 Bonding | Hood annealing | The residual iron powder on the surface of the steel coil is reduced to iron due to long-term heating in a full hydrogen atmosphere. In addition, the bonding is also related to the winding tension and cooling rate.
    2 Surface carbon black | hood annealing | Under full hydrogen high temperature atmosphere, the residual rolling oil on the steel surface decomposes to form carbon black deposited on the surface of the steel coil
    3 Rust and Corrosion | Steel Coil Storage and Transportation Process | Poor quality of anti-rust oil, uncoated anti-rust oil or insufficient amount of oil, etc., or high humidity in storage environment
    4 Underpickling | Pickling | The performance is that the iron oxide scale has not been washed off
    5 Over-pickling | Pickling | It is manifested by clear rolling lines visible on the surface of the substrate
    Second, the shape defect
    1 Beveling | Pickling, finishing, etc. | Refers to beveling when cutting steel coils or strips
    2 Sickle bending | Cold rolling, smoothing and smoothing | The rolling force on both sides of the strip is unbalanced, the rolling force response time lags or the roll gap is not uniform (the roll gap is not well adjusted) or the raw material density and hardness are not uniform
    3 Wave shape (subdivided into unilateral waves, bilateral waves, medium waves, oblique waves, etc.) | Cold rolling, smoothing and smoothing | Uneven density and hardness of raw materials, unresponsive adjustment of rolling force and bending force during rolling Or it is not allowed, the tension of the strip steel is too large, and the difference between the upper and lower roll diameters will also cause waves.
    4 Ladle | Hot rolling, cold rolling, smoothing and smoothing | Uneven density or hardness in the thickness direction of the raw material, resulting in uneven plasticity on the upper and lower sides of the steel plate. 3. Coil defects
    1 Tower type | Curl process | Caused by low curling precision of the coiler
    2 Drum package | Crimping process | The ultra-thin edges of the steel strip and the bulging of the steel coil during the continuous crimping process
    3 Drum ears | Crimping process | For galvanized coils, if there are extra thick edges, the steel coil may bulge at both ends during coiling
    4. Size defects
    1 Thickness deviation | Rolling process | Inaccurate rolling control, etc.
    2 Width short rule | Edge cutting process | Causes of inaccurate edge cutting or defect of raw material edge
    3 Too long length | Steel plate cutting process | Reasons for control accuracy, etc.
    Surface defects of hot dip galvanized steel sheet and steel strip
    1 Zinc granules | Hot galvanizing process | The bottom slag is mechanically stirred or floated due to the high temperature of the zinc solution, which adheres to the surface of the galvanized sheet and forms the zinc-iron compound FeZn10 during the cooling process
    2 Thick edges | Hot galvanizing process | Poor angle adjustment of the air knife, which causes counter-blowing to form a circumfluence; in addition, due to the part of the side air flowing out of the part, the blowing pressure is not enough, and it will also cause thick-edge defects
    3 Gray galvanized layer | Hot galvanized process | During the cooling phase transformation, if the zinc-iron alloy layer grows quickly to make the surface pure zinc layer disappear, that is, there is no zinc crystal pattern and it appears gray. It is generally believed that if the Si content in the steel is greater than 0.1%, it will promote the rapid growth of the zinc-iron alloy layer.
    4 Air knife streaks | Hot galvanizing process | Due to partial clogging of the air knife gap (such as clogging caused by zinc liquid splash), raised band marks are generated at the corresponding positions of the strip; the coating layer where the air knife streaks occur will seriously exceed thick
    5 Zinc protrusions | Hot galvanizing process | Due to the low temperature of the zinc solution or the high aluminum content in the zinc solution, special zinc crystals occur during the cooling phase transformation process, showing bright dendritic stripes and protruding the zinc layer (zinc protrusions)
    6 Shell-shaped surface | Hot-dip galvanizing process | On the surface of the galvanized sheet, bright zinc crystals in the shape of shells or scales appear, showing certain zinc fluctuations and often accompanied by zinc protrusions; the reasons are low temperature of the zinc solution and aluminum content in the zinc solution high
    7 Strip pattern | Hot-dip galvanizing process | Scattered outward at about 45 ° on the edge of the strip, forming regular dendritic crystal stripes. It often occurs in galvanized coils with a strip thickness less than 1 mm and a zinc layer weight greater than 275 g / m2. The reason is currently unclear
    8 Zinc wave | Hot galvanizing process | The low aluminum content in the zinc solution and the high temperature of the zinc solution make the zinc solution less viscous and more fluid but produce thick coatings that produce wave-like ripples. This zinc fluctuation forms Uneven thickness of galvanized layer
    9 Air knife scratches | Hot dip galvanizing process | Bad shape or air knife nozzle is too close to the strip to scratch the strip
    10 Jitter streaks | Hot-dip galvanizing process | If there are surface defects on sunken rollers, smoothing rollers or other rollers, they are periodically reflected on the surface of the galvanized sheet
    11 Zinc scar on sinking roller | Hot galvanizing process | Zinc slag is pressed onto the upper surface of the steel strip by the sinking roller and it is difficult to be blown off after passing through the air knife to form scar on the upper surface of the strip
    12 Coiling wrinkles | Coiling process of galvanized steel strip | During coiling, horizontal wrinkles are produced across the entire strip width. The main reason is that the tensile coefficient and flatness are insufficient
    13 Finishing | Finishing process | The finishing pressure is too large or the tension is too low
    14 Passivation spots | passivation process | passivation solution not blown dry or not squeezed out
    15 White rust | Storage and transportation process | The moisture stored in the surface area of ​​the steel belt is not lost in time or the passivation effect is not good
    16 Unsatisfactory roughness | hot dip galvanizing process | smoothing roller wear severe
    17 Wave edge | Hot dip galvanized | Insufficient tension correction factor, thick edge during coiling, severe wave shape on the original plate, etc. may cause wave shape
    if you want to learn more, please refer to PTJ Machining

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